diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 80a83337..92cf836c 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -17,6 +17,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          filter: tree:0
       - name: Setup .NET 9.0
         uses: actions/setup-dotnet@v2
         with:
@@ -29,10 +32,6 @@ jobs:
         uses: actions/setup-dotnet@v2
         with:
           dotnet-version: 6.0.x
-      - name: Setup .NET 3.1
-        uses: actions/setup-dotnet@v2
-        with:
-          dotnet-version: 3.1.x
       - name: Restore tools
         run: dotnet tool restore
       - name: Run the build script
diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index 33961d4b..47bafee1 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -23,6 +23,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          filter: tree:0
       - name: Setup .NET 9.0
         uses: actions/setup-dotnet@v2
         with:
@@ -35,10 +38,6 @@ jobs:
         uses: actions/setup-dotnet@v2
         with:
           dotnet-version: 6.0.x
-      - name: Setup .NET 3.1
-        uses: actions/setup-dotnet@v2
-        with:
-          dotnet-version: 3.1.x
       - name: Restore tools
         run: dotnet tool restore
       - name: Run the build script
diff --git a/src/TrueLayer/Mandates/IMandatesApi.cs b/src/TrueLayer/Mandates/IMandatesApi.cs
index 41d0c65a..4e8e1ab3 100644
--- a/src/TrueLayer/Mandates/IMandatesApi.cs
+++ b/src/TrueLayer/Mandates/IMandatesApi.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Threading;
 using System.Threading.Tasks;
 using OneOf;
@@ -28,11 +29,15 @@ public interface IMandatesApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
+        /// </param>
+        /// <param name="cancellationToken">The cancellation token to cancel the operation
         /// </param>
-        /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<CreateMandateResponse>> CreateMandate(
-            CreateMandateRequest mandateRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreateMandateRequest mandateRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets a mandate
@@ -42,7 +47,24 @@ Task<ApiResponse<CreateMandateResponse>> CreateMandate(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<MandateDetailUnion>> GetMandate(
-            string mandateId, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
+
+        /// <summary>
+        /// Generates a link to the TrueLayer hosted payment page
+        /// </summary>
+        /// <param name="mandateId">The mandate identifier</param>
+        /// <param name="resourceToken">The resource token, returned from <see cref="CreateMandate"/></param>
+        /// <param name="returnUri">
+        /// Your return URI to which the end user will be redirected after the mandate is completed.
+        /// Note this should be configured in the TrueLayer console under your application settings.
+        /// </param>
+        /// <returns>The HPP link you can redirect the end user to</returns>
+        string CreateHostedPaymentPageLink(
+            string mandateId,
+            string resourceToken,
+            Uri returnUri);
 
         /// <summary>
         /// Lists mandates for a user
@@ -52,7 +74,9 @@ Task<ApiResponse<MandateDetailUnion>> GetMandate(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
-            ListMandatesQuery query, MandateType mandateType, CancellationToken cancellationToken = default);
+            ListMandatesQuery query,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Start the authorization flow for a mandate.
@@ -63,11 +87,16 @@ Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
-            string mandateId, StartAuthorizationFlowRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            StartAuthorizationFlowRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Submit the provider details selected by the PSU.
@@ -78,11 +107,16 @@ Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
-            string mandateId, SubmitProviderSelectionRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            SubmitProviderSelectionRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Submit the consent given by the user
@@ -95,7 +129,11 @@ Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the authorization flow action details if successful, otherwise problem details</returns>
-        Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+        Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Get Confirmation Of Funds
@@ -107,7 +145,11 @@ Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
-            string mandateId, int amountInMinor, string currency, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            int amountInMinor,
+            string currency,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets a mandates constraints
@@ -117,18 +159,26 @@ Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the mandate if successful, otherwise problem details</returns>
         Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(
-            string mandateId, MandateType mandateType, CancellationToken cancellationToken = default);
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Revoke mandate
         /// </summary>
         /// <param name="mandateId">The id of the mandate</param>
+        /// <param name="mandateType">The type of the mandate. Either sweeping or commercial</param>
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payment details if successful, otherwise problem details</returns>
-        Task<ApiResponse> RevokeMandate(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default);
+        Task<ApiResponse> RevokeMandate(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Mandates/MandatesApi.cs b/src/TrueLayer/Mandates/MandatesApi.cs
index 505fe239..b79524be 100644
--- a/src/TrueLayer/Mandates/MandatesApi.cs
+++ b/src/TrueLayer/Mandates/MandatesApi.cs
@@ -6,6 +6,7 @@
 using TrueLayer.Extensions;
 using TrueLayer.Mandates.Model;
 using TrueLayer.Models;
+using TrueLayer.Payments;
 
 namespace TrueLayer.Mandates
 {
@@ -25,12 +26,14 @@ internal class MandatesApi : IMandatesApi
         private readonly TrueLayerOptions _options;
         private readonly Uri _baseUri;
         private readonly IAuthApi _auth;
+        private readonly HppLinkBuilder _hppLinkBuilder;
 
         public MandatesApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options)
         {
             _apiClient = apiClient.NotNull(nameof(apiClient));
             _options = options.NotNull(nameof(options));
             _auth = auth.NotNull(nameof(auth));
+            _hppLinkBuilder = new HppLinkBuilder(options.Payments?.HppUri, options.UseSandbox ?? true);
 
             options.Payments.NotNull(nameof(options.Payments))!.Validate();
 
@@ -39,10 +42,13 @@ public MandatesApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandateRequest mandateRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(
+            CreateMandateRequest mandateRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             mandateRequest.NotNull(nameof(mandateRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var mandateType = mandateRequest.Mandate.Match(
                 vrpCommercial => vrpCommercial.Type,
                 vrpSweeping => vrpSweeping.Type);
@@ -56,7 +62,7 @@ public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandat
             return await _apiClient.PostAsync<CreateMandateResponse>(
                 _baseUri,
                 mandateRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -65,7 +71,10 @@ public async Task<ApiResponse<CreateMandateResponse>> CreateMandate(CreateMandat
 
         //TODO: is it correct that this method expects a mandate type?
         /// <inheritdoc />
-        public async Task<ApiResponse<MandateDetailUnion>> GetMandate(string mandateId, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<MandateDetailUnion>> GetMandate(
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -85,7 +94,14 @@ public async Task<ApiResponse<MandateDetailUnion>> GetMandate(string mandateId,
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(ListMandatesQuery query, MandateType mandateType, CancellationToken cancellationToken = default)
+        public string CreateHostedPaymentPageLink(string mandateId, string resourceToken, Uri returnUri)
+            => _hppLinkBuilder.Build(mandateId, resourceToken, returnUri);
+
+        /// <inheritdoc />
+        public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListMandates(
+            ListMandatesQuery query,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
@@ -108,12 +124,17 @@ public async Task<ApiResponse<ResourceCollection<MandateDetailUnion>>> ListManda
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(string mandateId, StartAuthorizationFlowRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
+            string mandateId,
+            StartAuthorizationFlowRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
             request.NotNull(nameof(request));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -124,7 +145,7 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.AuthorizationFlow),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -132,12 +153,17 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(string mandateId, SubmitProviderSelectionRequest request, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelection(
+            string mandateId,
+            SubmitProviderSelectionRequest request,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
             request.NotNull(nameof(request));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -148,18 +174,22 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitProviderSelecti
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.ProviderSelection),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
+
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest($"recurring_payments:{mandateType.AsString()}"), cancellationToken);
 
             if (!authResponse.IsSuccessful)
@@ -170,7 +200,7 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.Consent),
                 null,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -178,7 +208,12 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> SubmitConsent(string
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(string mandateId, int amountInMinor, string currency, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOfFunds(
+            string mandateId,
+            int amountInMinor,
+            string currency,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -198,7 +233,10 @@ public async Task<ApiResponse<GetConfirmationOfFundsResponse>> GetConfirmationOf
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(string mandateId, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(
+            string mandateId,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -218,7 +256,11 @@ public async Task<ApiResponse<GetConstraintsResponse>> GetMandateConstraints(str
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse> RevokeMandate(string mandateId, string idempotencyKey, MandateType mandateType, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse> RevokeMandate(
+            string mandateId,
+            string? idempotencyKey,
+            MandateType mandateType,
+            CancellationToken cancellationToken = default)
         {
             mandateId.NotNullOrWhiteSpace(nameof(mandateId));
             mandateId.NotAUrl(nameof(mandateId));
@@ -233,7 +275,7 @@ public async Task<ApiResponse> RevokeMandate(string mandateId, string idempotenc
             return await _apiClient.PostAsync(
                 _baseUri.Append(mandateId).Append(MandatesEndpoints.Revoke),
                 null,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
diff --git a/src/TrueLayer/Payments/IPaymentsApi.cs b/src/TrueLayer/Payments/IPaymentsApi.cs
index a8ff9a59..e2acba80 100644
--- a/src/TrueLayer/Payments/IPaymentsApi.cs
+++ b/src/TrueLayer/Payments/IPaymentsApi.cs
@@ -42,11 +42,14 @@ public interface IPaymentsApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created payment if successful, otherwise problem details</returns>
         Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
-            CreatePaymentRequest paymentRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreatePaymentRequest paymentRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets the details of an existing payment
@@ -54,7 +57,9 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// <param name="id">The payment identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payment details if successful, otherwise problem details</returns>
-        Task<ApiResponse<GetPaymentUnion>> GetPayment(string id, CancellationToken cancellationToken = default);
+        Task<ApiResponse<GetPaymentUnion>> GetPayment(
+            string id,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Generates a link to the TrueLayer hosted payment page
@@ -66,7 +71,10 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// Note this should be configured in the TrueLayer console under your application settings.
         /// </param>
         /// <returns>The HPP link you can redirect the end user to</returns>
-        string CreateHostedPaymentPageLink(string paymentId, string paymentToken, Uri returnUri);
+        string CreateHostedPaymentPageLink(
+            string paymentId,
+            string paymentToken,
+            Uri returnUri);
 
         /// <summary>
         /// Start the authorization flow for a payment.
@@ -75,13 +83,14 @@ Task<ApiResponse<CreatePaymentUnion>> CreatePayment(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="request">The start authorization request details</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns></returns>
         Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
             string paymentId,
-            string idempotencyKey,
+            string? idempotencyKey,
             StartAuthorizationFlowRequest request,
             CancellationToken cancellationToken = default);
 
@@ -92,12 +101,14 @@ Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="request">The create payment refund request</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The id of the created refund</returns>
-        Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymentId,
-            string idempotencyKey,
+        Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
+            string paymentId,
+            string? idempotencyKey,
             CreatePaymentRefundRequest request,
             CancellationToken cancellationToken = default);
 
@@ -107,7 +118,8 @@ Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymen
         /// <param name="paymentId">The payment identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The list of refunds for a payment.</returns>
-        Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(string paymentId,
+        Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(
+            string paymentId,
             CancellationToken cancellationToken = default);
 
         /// <summary>
@@ -117,7 +129,8 @@ Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(string paymentI
         /// <param name="refundId">The refund identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>The details of the selected refund</returns>
-        Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
+        Task<ApiResponse<RefundUnion>> GetPaymentRefund(
+            string paymentId,
             string refundId,
             CancellationToken cancellationToken = default);
 
@@ -128,9 +141,13 @@ Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>HTTP 202 Accepted if successful, otherwise problem details.</returns>
-        Task<ApiResponse> CancelPayment(string paymentId, string idempotencyKey, CancellationToken cancellationToken = default);
+        Task<ApiResponse> CancelPayment(
+            string paymentId,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs b/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
index b6140063..d3a84cab 100644
--- a/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
+++ b/src/TrueLayer/Payments/Model/CreatePaymentRefundRequest.cs
@@ -2,6 +2,7 @@
 
 namespace TrueLayer.Payments.Model;
 
-public record CreatePaymentRefundRequest(string Reference,
+public record CreatePaymentRefundRequest(
+    string Reference,
     uint? AmountInMinor = null,
     Dictionary<string, string>? Metadata = null);
diff --git a/src/TrueLayer/Payments/PaymentsApi.cs b/src/TrueLayer/Payments/PaymentsApi.cs
index 958a6ecd..d5e092b9 100644
--- a/src/TrueLayer/Payments/PaymentsApi.cs
+++ b/src/TrueLayer/Payments/PaymentsApi.cs
@@ -55,10 +55,9 @@ public PaymentsApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRequest paymentRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRequest paymentRequest, string? idempotencyKey = null, CancellationToken cancellationToken = default)
         {
             paymentRequest.NotNull(nameof(paymentRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest(AuthorizationScope.Payments), cancellationToken);
 
@@ -70,7 +69,7 @@ public async Task<ApiResponse<CreatePaymentUnion>> CreatePayment(CreatePaymentRe
             return await _apiClient.PostAsync<CreatePaymentUnion>(
                 _baseUri,
                 paymentRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
@@ -105,12 +104,11 @@ public string CreateHostedPaymentPageLink(string paymentId, string paymentToken,
         /// <inheritdoc />
         public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlow(
             string paymentId,
-            string idempotencyKey,
+            string? idempotencyKey,
             StartAuthorizationFlowRequest request,
             CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
             request.NotNull(nameof(request));
 
             var authResponse = await _auth.GetAuthToken(
@@ -124,15 +122,18 @@ public async Task<ApiResponse<AuthorizationResponseUnion>> StartAuthorizationFlo
             return await _apiClient.PostAsync<AuthorizationResponseUnion>(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.AuthorizationFlow),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(string paymentId,
-            string idempotencyKey, CreatePaymentRefundRequest request, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
+            string paymentId,
+            string? idempotencyKey,
+            CreatePaymentRefundRequest request,
+            CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
             request.NotNull(nameof(request));
@@ -148,14 +149,15 @@ public async Task<ApiResponse<CreatePaymentRefundResponse>> CreatePaymentRefund(
             return await _apiClient.PostAsync<CreatePaymentRefundResponse>(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.Refunds),
                 request,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(string paymentId,
+        public async Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(
+            string paymentId,
             CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
@@ -175,8 +177,10 @@ public async Task<ApiResponse<ListPaymentRefundsResponse>> ListPaymentRefunds(st
             );
         }
 
-        public async Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
-            string refundId, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<RefundUnion>> GetPaymentRefund(
+            string paymentId,
+            string refundId,
+            CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
             refundId.NotNullOrWhiteSpace(nameof(refundId));
@@ -196,10 +200,12 @@ public async Task<ApiResponse<RefundUnion>> GetPaymentRefund(string paymentId,
             );
         }
 
-        public async Task<ApiResponse> CancelPayment(string paymentId, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse> CancelPayment(
+            string paymentId,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             paymentId.NotNullOrWhiteSpace(nameof(paymentId));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
             var authResponse = await _auth.GetAuthToken(
                 new GetAuthTokenRequest(AuthorizationScope.Payments), cancellationToken);
@@ -211,7 +217,7 @@ public async Task<ApiResponse> CancelPayment(string paymentId, string idempotenc
 
             return await _apiClient.PostAsync(
                 _baseUri.Append(paymentId).Append(PaymentsEndpoints.Cancel),
-                idempotencyKey: idempotencyKey,
+                idempotencyKey: idempotencyKey ?? Guid.NewGuid().ToString(),
                 accessToken: authResponse.Data!.AccessToken,
                 signingKey: _options.Payments!.SigningKey,
                 cancellationToken: cancellationToken);
diff --git a/src/TrueLayer/Payouts/IPayoutsApi.cs b/src/TrueLayer/Payouts/IPayoutsApi.cs
index d1266268..6ecb7021 100644
--- a/src/TrueLayer/Payouts/IPayoutsApi.cs
+++ b/src/TrueLayer/Payouts/IPayoutsApi.cs
@@ -25,11 +25,14 @@ public interface IPayoutsApi
         /// <param name="idempotencyKey">
         /// An idempotency key to allow safe retrying without the operation being performed multiple times.
         /// The value should be unique for each operation, e.g. a UUID, with the same key being sent on a retry of the same request.
+        /// If not provided an idempotency key is automatically generated.
         /// </param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes details of the created payout if successful, otherwise problem details</returns>
         Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
-            CreatePayoutRequest payoutRequest, string idempotencyKey, CancellationToken cancellationToken = default);
+            CreatePayoutRequest payoutRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Gets the details of an existing payment
@@ -37,6 +40,8 @@ Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
         /// <param name="id">The payout identifier</param>
         /// <param name="cancellationToken">The cancellation token to cancel the operation</param>
         /// <returns>An API response that includes the payout details if successful, otherwise problem details</returns>
-        Task<ApiResponse<GetPayoutUnion>> GetPayout(string id, CancellationToken cancellationToken = default);
+        Task<ApiResponse<GetPayoutUnion>> GetPayout(
+            string id,
+            CancellationToken cancellationToken = default);
     }
 }
diff --git a/src/TrueLayer/Payouts/PayoutsApi.cs b/src/TrueLayer/Payouts/PayoutsApi.cs
index 937a7041..a39232a4 100644
--- a/src/TrueLayer/Payouts/PayoutsApi.cs
+++ b/src/TrueLayer/Payouts/PayoutsApi.cs
@@ -37,10 +37,12 @@ public PayoutsApi(IApiClient apiClient, IAuthApi auth, TrueLayerOptions options)
         }
 
         /// <inheritdoc />
-        public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(CreatePayoutRequest payoutRequest, string idempotencyKey, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(
+            CreatePayoutRequest payoutRequest,
+            string? idempotencyKey = null,
+            CancellationToken cancellationToken = default)
         {
             payoutRequest.NotNull(nameof(payoutRequest));
-            idempotencyKey.NotNullOrWhiteSpace(nameof(idempotencyKey));
 
             var authResponse = await _auth.GetAuthToken(new GetAuthTokenRequest(AuthorizationScope.Payments), cancellationToken);
 
@@ -52,14 +54,16 @@ public async Task<ApiResponse<CreatePayoutResponse>> CreatePayout(CreatePayoutRe
             return await _apiClient.PostAsync<CreatePayoutResponse>(
                 _baseUri,
                 payoutRequest,
-                idempotencyKey,
+                idempotencyKey ?? Guid.NewGuid().ToString(),
                 authResponse.Data!.AccessToken,
                 _options.Payments!.SigningKey,
                 cancellationToken
             );
         }
 
-        public async Task<ApiResponse<GetPayoutUnion>> GetPayout(string id, CancellationToken cancellationToken = default)
+        public async Task<ApiResponse<GetPayoutUnion>> GetPayout(
+            string id,
+            CancellationToken cancellationToken = default)
         {
             id.NotNullOrWhiteSpace(nameof(id));
             id.NotAUrl(nameof(id));
diff --git a/test/TrueLayer.AcceptanceTests/MandatesTests.cs b/test/TrueLayer.AcceptanceTests/MandatesTests.cs
index ddfc1b26..07ac54b1 100644
--- a/test/TrueLayer.AcceptanceTests/MandatesTests.cs
+++ b/test/TrueLayer.AcceptanceTests/MandatesTests.cs
@@ -38,10 +38,10 @@ public class MandatesTests : IClassFixture<ApiTestFixture>
     {
         private readonly ApiTestFixture _fixture;
         private TrueLayerOptions configuration;
-        public string RETURN_URI = "http://localhost:3000/callback";
-        public static string PROVIDER_ID = "ob-uki-mock-bank-sbox"; // Beta provider in closed access, requires a whitelisted ClientId.
-        public static string COMMERCIAL_PROVIDER_ID = "ob-natwest-vrp-sandbox"; // Provider to satisfy commercial mandates creation.
-        public static AccountIdentifier.SortCodeAccountNumber accountIdentifier = new("140662", "10003957");
+        private const string ReturnUri = "http://localhost:3000/callback";
+        private const string ProviderId = "ob-uki-mock-bank-sbox"; // Beta provider in closed access, requires a whitelisted ClientId.
+        private const string CommercialProviderId = "mock-payments-gb-redirect"; // Provider to satisfy commercial mandates creation.
+        private static AccountIdentifier.SortCodeAccountNumber accountIdentifier = new("140662", "10003957");
 
         public MandatesTests(ApiTestFixture fixture)
         {
@@ -117,7 +117,7 @@ public async Task Can_start_authorization(CreateMandateRequest mandateRequest)
             var mandateId = createResponse.Data!.Id;
             StartAuthorizationFlowRequest authorizationRequest = new(
                 new ProviderSelectionRequest(),
-                new Redirect(new Uri(RETURN_URI)));
+                new Redirect(new Uri(ReturnUri)));
 
             // Act
             var response = await _fixture.Client.Mandates.StartAuthorizationFlow(
@@ -140,10 +140,10 @@ public async Task Can_submit_provider_selection(CreateMandateRequest mandateRequ
             var createResponse = await _fixture.Client.Mandates.CreateMandate(
                 mandateRequest, idempotencyKey: Guid.NewGuid().ToString());
             var mandateId = createResponse.Data!.Id;
-            SubmitProviderSelectionRequest request = new(COMMERCIAL_PROVIDER_ID);
+            SubmitProviderSelectionRequest request = new(CommercialProviderId);
             StartAuthorizationFlowRequest authorizationRequest = new(
                 new ProviderSelectionRequest(),
-                new Redirect(new Uri(RETURN_URI)));
+                new Redirect(new Uri(ReturnUri)));
             await _fixture.Client.Mandates.StartAuthorizationFlow(
                 mandateId, authorizationRequest, idempotencyKey: Guid.NewGuid().ToString(), MandateType.Sweeping);
             // Act
@@ -161,23 +161,23 @@ await _fixture.Client.Mandates.StartAuthorizationFlow(
         public async Task Can_submit_consent(CreateMandateRequest mandateRequest)
         {
             // Arrange
-            var createResponse = await _fixture.Client.Mandates.CreateMandate(
-                mandateRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var createResponse = await _fixture.Client.Mandates.CreateMandate(mandateRequest);
 
             var mandateId = createResponse.Data!.Id;
             var mandateType = mandateRequest.Mandate.IsT0 ? MandateType.Commercial : MandateType.Sweeping;
 
-            StartAuthorizationFlowRequest authorizationRequest = new(
+            var authorizationRequest = new StartAuthorizationFlowRequest(
                 new ProviderSelectionRequest(),
-                new Redirect(new Uri(RETURN_URI)),
+                new Redirect(new Uri(ReturnUri)),
                 new Consent());
 
             await _fixture.Client.Mandates.StartAuthorizationFlow(
                 mandateId, authorizationRequest, idempotencyKey: Guid.NewGuid().ToString(), mandateType);
 
-            SubmitProviderSelectionRequest submitProviderRequest = new(mandateRequest.Mandate.Match(
-                c => COMMERCIAL_PROVIDER_ID,
-                s => PROVIDER_ID));
+            var submitProviderRequest = new SubmitProviderSelectionRequest(
+                mandateRequest.Mandate.Match(
+                    commercial => CommercialProviderId,
+                    sweeping => ProviderId));
 
             await _fixture.Client.Mandates.SubmitProviderSelection(
                 mandateId, submitProviderRequest, idempotencyKey: Guid.NewGuid().ToString(), mandateType);
@@ -200,7 +200,7 @@ public async Task Can_Get_Funds(CreateMandateRequest mandateRequest)
             var mandateId = createResponse.Data!.Id;
             StartAuthorizationFlowRequest authorizationRequest = new(
                 new ProviderSelectionRequest(),
-                new Redirect(new Uri(RETURN_URI)));
+                new Redirect(new Uri(ReturnUri)));
 
             // Act
             var response = await _fixture.Client.Mandates.StartAuthorizationFlow(
@@ -356,9 +356,9 @@ private async Task<string> CreateAuthorizedSweepingMandate(CreateMandateRequest
 
             createResponse.StatusCode.Should().Be(HttpStatusCode.Created);
 
-            StartAuthorizationFlowRequest authorizationRequest = new(
+            var  authorizationRequest = new StartAuthorizationFlowRequest(
                 new ProviderSelectionRequest(),
-                new Redirect(new Uri(RETURN_URI)));
+                new Redirect(new Uri(ReturnUri)));
 
             var startAuthResponse = await _fixture.Client.Mandates.StartAuthorizationFlow(
                 mandateId, authorizationRequest, idempotencyKey: Guid.NewGuid().ToString(), MandateType.Sweeping);
@@ -369,64 +369,64 @@ private async Task<string> CreateAuthorizedSweepingMandate(CreateMandateRequest
 
         public static IEnumerable<object[]> CreateTestSweepingPreselectedMandateRequests()
         {
-            yield return new[]
-            {
+            yield return
+            [
                 CreateTestMandateRequest(MandateUnion.FromT1(new Mandate.VRPSweepingMandate(
                     "sweeping",
-                    ProviderUnion.FromT1(new Mandates.Model.Provider.Preselected("preselected", PROVIDER_ID)),
+                    ProviderUnion.FromT1(new Mandates.Model.Provider.Preselected("preselected", ProviderId)),
                     new Mandates.Model.Beneficiary.ExternalAccount(
                         "external_account",
                         "Bob NET SDK",
-                        AccountIdentifierUnion.FromT0(accountIdentifier))))),
-            };
+                        AccountIdentifierUnion.FromT0(accountIdentifier)))))
+            ];
         }
 
         public static IEnumerable<object[]> CreateTestCommercialPreselectedMandateRequests()
         {
-            yield return new[]
-            {
+            yield return
+            [
                 CreateTestMandateRequest(MandateUnion.FromT0(new Mandate.VRPCommercialMandate(
                     "commercial",
-                    ProviderUnion.FromT1(new Mandates.Model.Provider.Preselected("preselected", COMMERCIAL_PROVIDER_ID)),
+                    ProviderUnion.FromT1(new Mandates.Model.Provider.Preselected("preselected", CommercialProviderId)),
                     new Mandates.Model.Beneficiary.ExternalAccount(
                         "external_account",
                         "My Bank Account",
-                        AccountIdentifierUnion.FromT0(accountIdentifier))))),
-            };
+                        AccountIdentifierUnion.FromT0(accountIdentifier)))))
+            ];
         }
 
         public static IEnumerable<object[]> CreateTestSweepingUserSelectedMandateRequests()
         {
-            yield return new[]
-            {
+            yield return
+            [
                 CreateTestMandateRequest(MandateUnion.FromT1(new Mandate.VRPSweepingMandate(
                     "sweeping",
                     ProviderUnion.FromT0(new Payments.Model.Provider.UserSelected
                     {
-                        Filter = new ProviderFilter {Countries = new[] {"GB"}, ReleaseChannel = "general_availability"},
+                        Filter = new ProviderFilter {Countries = ["GB"], ReleaseChannel = "alpha"},
                     }),
                     new Mandates.Model.Beneficiary.ExternalAccount(
                         "external_account",
                         "My Bank Account",
-                        AccountIdentifierUnion.FromT0(accountIdentifier))))),
-            };
+                        AccountIdentifierUnion.FromT0(accountIdentifier)))))
+            ];
         }
 
         public static IEnumerable<object[]> CreateTestCommercialUserSelectedMandateRequests()
         {
-            yield return new[]
-            {
+            yield return
+            [
                 CreateTestMandateRequest(MandateUnion.FromT0(new Mandate.VRPCommercialMandate(
                     "commercial",
                     ProviderUnion.FromT0(new Payments.Model.Provider.UserSelected
                     {
-                        Filter = new ProviderFilter {Countries = new[] {"GB"}, ReleaseChannel = "general_availability"},
+                        Filter = new ProviderFilter {Countries = ["GB"], ReleaseChannel = "alpha"},
                     }),
                     new Mandates.Model.Beneficiary.ExternalAccount(
                         "external_account",
                         "My Bank Account",
-                        AccountIdentifierUnion.FromT0(accountIdentifier))))),
-            };
+                        AccountIdentifierUnion.FromT0(accountIdentifier)))))
+            ];
         }
     }
 }
diff --git a/test/TrueLayer.AcceptanceTests/PaymentTests.cs b/test/TrueLayer.AcceptanceTests/PaymentTests.cs
index b6c66ec9..7b438e37 100644
--- a/test/TrueLayer.AcceptanceTests/PaymentTests.cs
+++ b/test/TrueLayer.AcceptanceTests/PaymentTests.cs
@@ -67,8 +67,7 @@ public PaymentTests(ApiTestFixture fixture)
     [MemberData(nameof(ExternalAccountPaymentRequests))]
     public async Task Can_Create_External_Account_Payment(CreatePaymentRequest paymentRequest)
     {
-        var response = await _fixture.Client.Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.Client.Payments.CreatePayment(paymentRequest);
 
         response.StatusCode.Should().Be(HttpStatusCode.Created);
         var authorizationRequired = response.Data.AsT0;
@@ -131,8 +130,7 @@ public async Task Can_Create_Merchant_Account_Gbp_Verification_Payment()
                 Verification = new Verification.Automated { RemitterName = true }
             });
 
-        var response = await _fixture.Client.Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.Client.Payments.CreatePayment(paymentRequest);
 
         response.StatusCode.Should().Be(HttpStatusCode.Created);
         var authorizationRequired = response.Data.AsT0;
@@ -239,8 +237,7 @@ public async Task GetPayment_Should_Return_Settled_Payment()
     [MemberData(nameof(ExternalAccountPaymentRequests))]
     public async Task Can_Get_Authorization_Required_Payment(CreatePaymentRequest paymentRequest)
     {
-        var response = await _fixture.Client.Payments.CreatePayment(
-            paymentRequest, idempotencyKey: Guid.NewGuid().ToString());
+        var response = await _fixture.Client.Payments.CreatePayment(paymentRequest);
 
         response.IsSuccessful.Should().BeTrue();
         response.Data.IsT0.Should().BeTrue();
@@ -312,7 +309,7 @@ public async Task Can_create_and_get_payment_refund()
         // Act && assert
         var createRefundResponse = await _fixture.Client.Payments.CreatePaymentRefund(
             paymentId: paymentId,
-            idempotencyKey: Guid.NewGuid().ToString(),
+            null,
             new CreatePaymentRefundRequest(Reference: "a-reference"));
         createRefundResponse.IsSuccessful.Should().BeTrue();
         createRefundResponse.Data!.Id.Should().NotBeNullOrWhiteSpace();
@@ -366,9 +363,7 @@ public async Task Can_Cancel_Payment()
         var paymentId = payment.Data.AsT0.Id;
 
         // act
-        var cancelPaymentResponse = await _fixture.Client.Payments.CancelPayment(
-            paymentId,
-            idempotencyKey: Guid.NewGuid().ToString());
+        var cancelPaymentResponse = await _fixture.Client.Payments.CancelPayment(paymentId);
 
         var getPaymentResponse = await _fixture.Client.Payments.GetPayment(paymentId);
 
diff --git a/test/TrueLayer.AcceptanceTests/PayoutTests.cs b/test/TrueLayer.AcceptanceTests/PayoutTests.cs
index a902530b..47f87861 100644
--- a/test/TrueLayer.AcceptanceTests/PayoutTests.cs
+++ b/test/TrueLayer.AcceptanceTests/PayoutTests.cs
@@ -26,8 +26,7 @@ public async Task Can_create_payout()
         {
             CreatePayoutRequest payoutRequest = CreatePayoutRequest();
 
-            var response = await _fixture.Client.Payouts.CreatePayout(
-                payoutRequest, idempotencyKey: Guid.NewGuid().ToString());
+            var response = await _fixture.Client.Payouts.CreatePayout(payoutRequest);
 
             response.StatusCode.Should().Be(HttpStatusCode.Accepted);
             response.Data.Should().NotBeNull();
@@ -73,11 +72,11 @@ public async Task InitializeAsync()
                 throw new InvalidOperationException("You must have a merchant account in order to perform a payout");
             }
 
-            _merchantAccount = accounts.Data.Items.Single(x => x.Currency == "GBP");
+            _merchantAccount = accounts.Data.Items.Single(x => x.Currency == Currencies.GBP);
         }
 
         private CreatePayoutRequest CreatePayoutRequest()
-            => new CreatePayoutRequest(
+            => new(
                 _merchantAccount!.Id,
                 100,
                 Currencies.GBP,
diff --git a/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj b/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
index b35f951e..663b6093 100644
--- a/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
+++ b/test/TrueLayer.AcceptanceTests/TrueLayer.AcceptanceTests.csproj
@@ -8,8 +8,8 @@
       <WarningsAsErrors>nullable;</WarningsAsErrors>
     </PropertyGroup>
     <ItemGroup>
-      <PackageReference Include="FluentAssertions" Version="6.12.2" />
-      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.11.1" />
+      <PackageReference Include="FluentAssertions" Version="7.0.0" />
+      <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
       <PackageReference Include="xunit" Version="2.9.2" />
       <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
diff --git a/test/TrueLayer.Tests/TrueLayer.Tests.csproj b/test/TrueLayer.Tests/TrueLayer.Tests.csproj
index 678d8008..96a328af 100644
--- a/test/TrueLayer.Tests/TrueLayer.Tests.csproj
+++ b/test/TrueLayer.Tests/TrueLayer.Tests.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
     <PropertyGroup>
-        <TargetFrameworks>net9.0;net8.0;net6.0;netcoreapp3.1</TargetFrameworks>
+        <TargetFrameworks>net9.0;net8.0;net6.0</TargetFrameworks>
         <IsPackable>false</IsPackable>
         <LangVersion>10.0</LangVersion>
         <Nullable>enable</Nullable>
@@ -17,7 +17,7 @@
             <PrivateAssets>all</PrivateAssets>
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
         </PackageReference>
-        <PackageReference Include="FluentAssertions" Version="6.12.2"/>
+        <PackageReference Include="FluentAssertions" Version="7.0.0" />
         <PackageReference Include="RichardSzalay.MockHttp" Version="7.0.0" />
         <PackageReference Include="Microsoft.Extensions.Configuration" Version="9.0.0" />
     </ItemGroup>