Update Unified billing for GA (#644)

docs/integrations/apps/unified-billing/index.mdx

@@ -14,4 +14,19 @@ The following scopes pertain directly to Unified Partner Billing. For a complete
 | Subscriptions | modify | `account_subscriptions_cancel` | View or cancel account-level subscriptions | [GraphQL Account API](/docs/graphql-account/users-overview) |
 | Subscriptions | read-only | `account_subscriptions_read` | View account-level subscriptions | [GraphQL Account API](/docs/graphql-account/users-overview) |
 | Checkouts | modify | `account_checkouts_create` | View or cancel account-level checkouts | [GraphQL Account API](/docs/graphql-account/users-overview) |
-| Checkouts | read-only | `account_checkouts_read` | View account-level checkouts | [GraphQL Account API](/docs/graphql-account/users-overview) |
+| Checkouts | read-only | `account_checkouts_read` | View account-level checkouts | [GraphQL Account API](/docs/graphql-account/users-overview) |
+
+
+### Gathering Information 
+
+Collect the following values to use later.
+
+| Value | Description | 
+|:--------|:-----------|
+| Authentication headers | To authenticate API requests, visit the [account center (Staging Zone)](https://login.staging.zone/login) and generate a new account-level API account. Note the X-Auth-Client and X-Auth-Token properties because you must include them in the request headers. You can't reaccess the credentials from this page, so save them somewhere safe. Use the following list of OAuth scopes to inform the scopes you select for the API account. | 
+| Partner ID | To retrieve the partner ID, sign in to the [staging partner portal (Impartner)](https://bigcommerce.stage.impartner.live/) and go to your account profile. |
+| Partner account UUID | To retrieve your partner account UUID, sign in to the [staging developer portal (Staging Zone)](https://login.staging.zone/login) and copy the Account UUID from the top nav bar. | 
+| Application ID | Create your app in the staging [developer portal (Staging Zone)](https://login.staging.zone/login) and record your application ID. Make sure to also input your partner information associated with the app, especially the partner ID from the [staging partner portal (Impartner)](https://bigcommerce.stage.impartner.live/). |
+| Merchant account UUID | To retrieve the merchant account UUID, send a request to [Get Store Information](https://developer.bigcommerce.com/docs/rest-management/store-information#get-store-information) endpoint and record the merchant's account_uuid from the response. | 
+
+