diff --git a/app/controllers/api/v1/base_controller.rb b/app/controllers/api/v1/base_controller.rb
index e0fc7e0..6c74396 100644
--- a/app/controllers/api/v1/base_controller.rb
+++ b/app/controllers/api/v1/base_controller.rb
@@ -35,7 +35,6 @@ class BaseController < ActionController::API
 
       private
 
-
       def decoded_token
         return @decoded_token if defined?(@decoded_token)
 
@@ -117,8 +116,6 @@ def require_user
         false
       end
 
-      private
-
       def find_user_from_token
         return unless decoded_token
         user_data = decoded_token[:user]
diff --git a/app/controllers/api/v1/saved_scenarios_controller.rb b/app/controllers/api/v1/saved_scenarios_controller.rb
index 16710f6..2116f06 100644
--- a/app/controllers/api/v1/saved_scenarios_controller.rb
+++ b/app/controllers/api/v1/saved_scenarios_controller.rb
@@ -68,7 +68,15 @@ def saved_scenario_params
       end
 
       def engine_client
-        MyEtm::Auth.engine_client(current_user)#, scopes: doorkeeper_token.scopes)
+        MyEtm::Auth.engine_client(current_user, active_version_tag, scopes: doorkeeper_token.scopes)
+      end
+
+      def active_version_tag
+        if Version.tags.include?(saved_scenario_params[:version].to_s)
+          saved_scenario_params[:version]
+        else
+          Version::DEFAULT_TAG
+        end
       end
     end
   end
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index f140b25..bbd39ff 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -7,7 +7,9 @@ class ApplicationController < ActionController::Base
   before_action :set_locale
   before_action :configure_sentry
   before_action :store_user_location!, if: :storable_location?
-  before_action :store_redirect_url
+  before_action :set_active_version_tag
+
+  helper_method :active_version_tag
 
   rescue_from CanCan::AccessDenied do |_exception|
     if current_user
@@ -36,8 +38,8 @@ def set_locale
       session[:locale] || http_accept_language.preferred_language_from(I18n.available_locales)
   end
 
-  def last_visited_page
-    redirect_to cookies[:last_visited_page] || root_path
+  def active_version_tag
+    session[:active_version_tag] || Version::DEFAULT_TAG
   end
 
   private
@@ -74,8 +76,8 @@ def configure_sentry
     end
   end
 
-  def engine_client
-    MyEtm::Auth.engine_client(current_user)
+  def engine_client(version_tag)
+    MyEtm::Auth.engine_client(current_user, version_tag)
   end
 
   # Internal: Renders a 404 page.
@@ -136,9 +138,14 @@ def turbo_alert(message = nil)
     )
   end
 
-  def store_redirect_url
-    if params[:redirect_url].present?
-      session[:redirect_url] = params[:redirect_url]
-    end
+  # Validates the version tag passed from the latest request and sets it in the
+  # session, so we can redirect back to that version later.
+  #
+  # TODO: somebody has to set this!
+  def set_active_version_tag
+    return unless params[:active_version]
+    return unless Version.tags.include?(params[:active_version].to_s)
+
+    session[:active_version_tag] = params[:active_version]
   end
 end
diff --git a/app/controllers/collections_controller.rb b/app/controllers/collections_controller.rb
index af573eb..8a1a455 100644
--- a/app/controllers/collections_controller.rb
+++ b/app/controllers/collections_controller.rb
@@ -75,7 +75,7 @@ def show
   # POST /collections/create_transition
   def create_transition
     result = CreateInterpolatedCollection.call(
-      engine_client,
+      engine_client(create_transition_params[:version]),
       current_user.saved_scenarios.find(create_transition_params[:saved_scenario_ids]),
       current_user
     )
@@ -120,8 +120,8 @@ def confirm_destroy
   # DELETE /collections/:id
   def destroy
     DeleteCollection.call(
-      engine_client,
-      current_user.collections.find(params.require(:id))
+      engine_client(@collection.version),
+      @collection
     )
 
     redirect_to collections_path
@@ -178,7 +178,7 @@ def create_collection_params
   end
 
   def create_transition_params
-    params.require(:collection).permit(:saved_scenario_ids)
+    params.require(:collection).permit(:version, :saved_scenario_ids)
   end
 
   def filter_params
diff --git a/app/controllers/passthru_controller.rb b/app/controllers/passthru_controller.rb
new file mode 100644
index 0000000..1b63a25
--- /dev/null
+++ b/app/controllers/passthru_controller.rb
@@ -0,0 +1,5 @@
+class PassthruController < ApplicationController
+  def last
+    redirect_to cookies[:etm_last_visited_page] || root_path
+  end
+end
\ No newline at end of file
diff --git a/app/controllers/saved_scenario_history_controller.rb b/app/controllers/saved_scenario_history_controller.rb
index 70448a2..4a79852 100644
--- a/app/controllers/saved_scenario_history_controller.rb
+++ b/app/controllers/saved_scenario_history_controller.rb
@@ -12,7 +12,10 @@ class SavedScenarioHistoryController < ApplicationController
 
   # GET /saved_scenarios/:id/history
   def index
-    version_tags_result = ApiScenario::VersionTags::FetchAll.call(engine_client, @saved_scenario)
+    version_tags_result = ApiScenario::VersionTags::FetchAll.call(
+      engine_client(@saved_scenario.version),
+      @saved_scenario
+    )
 
     if version_tags_result.successful?
       @history = SavedScenarioHistoryPresenter.present(@saved_scenario, version_tags_result.value)
@@ -32,7 +35,7 @@ def index
   # PUT /saved_scenarios/:id/history/:scenario_id
   def update
     result = ApiScenario::VersionTags::Update.call(
-      engine_client,
+      engine_client(@saved_scenario.version),
       params[:scenario_id],
       update_params[:description]
     )
diff --git a/app/controllers/saved_scenario_users_controller.rb b/app/controllers/saved_scenario_users_controller.rb
index af78896..3cba662 100644
--- a/app/controllers/saved_scenario_users_controller.rb
+++ b/app/controllers/saved_scenario_users_controller.rb
@@ -37,7 +37,10 @@ def new
   # POST /saved_scenarios/:saved_scenario_id/users
   def create
     result = CreateSavedScenarioUser.call(
-      engine_client, @saved_scenario, current_user.name, scenario_user_params
+      engine_client(@saved_scenario.version),
+      @saved_scenario,
+      current_user.name,
+      scenario_user_params
     )
 
     if result.successful?
@@ -71,7 +74,7 @@ def create
   # PUT /saved_scenarios/:saved_scenario_id/users/:id
   def update
     result = UpdateSavedScenarioUser.call(
-      engine_client,
+      engine_client(@saved_scenario.version),
       @saved_scenario,
       @saved_scenario_user,
       scenario_user_params[:role_id]&.to_i
@@ -110,7 +113,11 @@ def confirm_destroy
   #
   # PUT /saved_scenarios/:saved_scenario_id/users/:id
   def destroy
-    result = DestroySavedScenarioUser.call(engine_client, @saved_scenario, @saved_scenario_user)
+    result = DestroySavedScenarioUser.call(
+      engine_client(@saved_scenario.version),
+      @saved_scenario,
+      @saved_scenario_user
+    )
 
     if result.successful?
       @saved_scenario.reload
diff --git a/app/controllers/saved_scenarios_controller.rb b/app/controllers/saved_scenarios_controller.rb
index 17d3c9a..8a17a8c 100644
--- a/app/controllers/saved_scenarios_controller.rb
+++ b/app/controllers/saved_scenarios_controller.rb
@@ -114,7 +114,7 @@ def publish
     @saved_scenario.update(private: false)
 
     ApiScenario::UpdatePrivacy.call_with_ids(
-      engine_client,
+      engine_client(@saved_scenario.version),
       @saved_scenario.all_scenario_ids,
       private: false
     )
@@ -127,7 +127,7 @@ def unpublish
     @saved_scenario.update(private: true)
 
     ApiScenario::UpdatePrivacy.call_with_ids(
-      engine_client,
+      engine_client(@saved_scenario.version),
       @saved_scenario.all_scenario_ids,
       private: true
     )
diff --git a/app/controllers/users/registrations_controller.rb b/app/controllers/users/registrations_controller.rb
index c151d94..abdfa66 100644
--- a/app/controllers/users/registrations_controller.rb
+++ b/app/controllers/users/registrations_controller.rb
@@ -57,7 +57,6 @@ def configure_account_update_params
     # Check if the user is already signed in and redirect back to client or to root.
     def check_already_authenticated
       return unless user_signed_in?
-        redirect_uri = session[:redirect_url].chomp('/')
         token = MyEtm::Auth.user_jwt(current_user, client_id: params[:client_id])
         redirect_url = URI(params[:redirect_url] || root_path)
         redirect_url.query = URI.encode_www_form(token: token)
@@ -71,7 +70,7 @@ def stats_for_destroy
         personal_access_tokens: current_user.personal_access_tokens.not_expired.count,
         oauth_applications: current_user.oauth_applications.count,
         collections: 0
-        # collections: current_user.collections.count
+        # collections: current_user.collections.count # TODO: Re-Implement
       }
     end
   end
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index 78ebdf8..2b0e55e 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -30,11 +30,11 @@ def format_staff_config(config, app)
     etengine_url = Settings.etengine.uri || "http://YOUR_ETENGINE_URL"
 
     format(config, app.attributes.symbolize_keys.merge(
-      myetm_url: root_url.chomp("/root"),
+      myetm_url: root_url.chomp("/"),
       etengine_url: etengine_url,
       etmodel_url: Settings.etmodel.uri || "http://YOUR_ETMODEL_URL",
       collections_url: Settings.collections.uri || "http://YOUR_COLLECTIONS_URL",
-      etengine_uid: Doorkeeper::Application.find_by(uri: etengine_url)&.uid || "YOUR_ETEngine_ID_HERE"
+      etengine_uid: Doorkeeper::Application.find_by(uri: etengine_url)&.uid || "YOUR_ETEngine_ID"
     ))
   end
 
diff --git a/app/models/version.rb b/app/models/version.rb
index 45a021e..ff5151c 100644
--- a/app/models/version.rb
+++ b/app/models/version.rb
@@ -1,8 +1,10 @@
 # frozen_string_literal: true
 
+# TODO: port to db and hook into OAuth apps. This is a mess and not nice to keep up for beta and pro!
 # A valid version of the ETM
 class Version
   URL = "energytransitionmodel.com".freeze
+  DEFAULT_TAG =  "latest"
 
   # Tag => prefix
   LIST = {
@@ -11,6 +13,12 @@ class Version
     "stable.02" => "stable2."
   }.freeze
 
+  LOCAL_URLS = {
+    "collections" => Settings.collections.uri,
+    "model" => Settings.etmodel.uri,
+    "engine" => Settings.etengine.uri
+  }.freeze
+
   # All available versions. Uses ActiveRecord syntax 'all' to
   # make future porting to db easier
   def self.all
@@ -21,26 +29,39 @@ def self.tags
     LIST.keys
   end
 
-  def self.model_url(tag)
-    "https://#{LIST[tag]}#{Version::URL}"
+  def self.collections_url(tag = nil)
+    build_url("collections", tag)
   end
 
-  def self.engine_url(tag)
-    "https://#{LIST[tag]}engine.#{Version::URL}"
+  def self.model_url(tag = nil)
+    build_url("model", tag)
   end
 
-  # TODO: Collections url
-
-  # TODO: urls for local development => Add a local version and
-  # exceptions for the urls
+  def self.engine_url(tag = nil)
+    build_url("engine", tag)
+  end
 
   def self.as_json(*)
     Version.tags.map do |tag|
       {
         tag: tag,
-        url: Version.model_url(tag),
-        engine_url: Version.engine_url(tag)
+        model_url: model_url(tag),
+        engine_url: engine_url(tag),
+        collections_url: collections_url(tag)
       }
     end
   end
+
+  private
+
+  def self.build_url(context, tag)
+    tag ||= DEFAULT_TAG
+    raise ArgumentError, "Invalid version tag: #{tag}" unless LIST.key?(tag)
+
+    if Rails.env.development?
+      LOCAL_URLS[context]
+    else
+      "https://#{LIST[tag]}#{context == 'model' ? '' : "#{context}."}#{URL}"
+    end
+  end
 end
diff --git a/app/services/create_staff_application.rb b/app/services/create_staff_application.rb
index 20d93e2..704f555 100644
--- a/app/services/create_staff_application.rb
+++ b/app/services/create_staff_application.rb
@@ -25,7 +25,7 @@ def self.call(user, app_config, uri: nil)
 
     # Update application attributes
     app.attributes = app_config.to_model_attributes.merge(
-      owner: user,
+      owner_id: user.id,
       uri: parsed_uri.to_s,
       redirect_uri: redirect_uri.to_s
     )
diff --git a/app/views/layouts/_buttons.html.haml b/app/views/layouts/_buttons.html.haml
index c1df0c8..78ac6d2 100644
--- a/app/views/layouts/_buttons.html.haml
+++ b/app/views/layouts/_buttons.html.haml
@@ -1,5 +1,5 @@
 .flex.py-5
   .flex.basis-full{class: 'lg:basis-3/4'}
-    - if cookies[:last_visited_page].present?
+    - if cookies[:etm_last_visited_page].present?
       .bg-gray-100.p-2.px-5.mr-0.ml-auto.rounded-md
-        = link_to t('continue_working'), last_visited_page_path, class: 'continue-button'
+        = link_to t('continue_working'), back_to_etm_path, class: 'continue-button'
diff --git a/app/views/layouts/_sidebar.html.haml b/app/views/layouts/_sidebar.html.haml
index 1faf8c2..db0e301 100644
--- a/app/views/layouts/_sidebar.html.haml
+++ b/app/views/layouts/_sidebar.html.haml
@@ -1,6 +1,5 @@
 .sidebar.fixed.top-0.bottom-0.overflow-y-auto.bg-midnight-300{class: 'lg:left-0 w-[300px]'}
-  -# Where does the logo refer to? REMEMBER LAST VERSION IN COOKIE
-  %a.logo.p-5.mb-3.inline-block.w-full.text-midnight-800
+  %a.logo.p-5.mb-3.inline-block.w-full.text-midnight-800{href: Version.model_url(active_version_tag)}
     = image_tag 'header/logo-round.png', class: 'h-8 inline mb-1 mr-2 hover:animate-spin'
     %span Energy Transition Model
 
diff --git a/config/initializers/doorkeeper.rb b/config/initializers/doorkeeper.rb
index 8e160c4..f7cac85 100644
--- a/config/initializers/doorkeeper.rb
+++ b/config/initializers/doorkeeper.rb
@@ -41,7 +41,7 @@
   #
   # access_token_class "Doorkeeper::AccessToken"
   # access_grant_class "Doorkeeper::AccessGrant"
-  application_class 'OAuthApplication'
+  application_class "OAuthApplication"
   #
   # Don't forget to include Doorkeeper ORM mixins into your custom models:
   #
diff --git a/config/routes.rb b/config/routes.rb
index 50cf62d..4cf8895 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -13,7 +13,7 @@
     mount Sidekiq::Web => '/sidekiq'
   end
 
-  get '/last_visited_page', to: 'application#last_visited_page', as: :last_visited_page
+  get '/passthru/last', to: 'passthru#last', as: :back_to_etm
 
   namespace :identity do
     get '/', to: redirect('/identity/profile')
diff --git a/lib/myetm/auth.rb b/lib/myetm/auth.rb
index 96f8ac6..bd3c610 100644
--- a/lib/myetm/auth.rb
+++ b/lib/myetm/auth.rb
@@ -53,31 +53,41 @@ def user_jwt(user = nil, scopes: [], client_id: nil)
     end
 
     # Returns a Faraday client for a user, which will send requests to the specified client app.
-    def client_app_client(user, client_app)
-      client_app_client ||= begin
-        Faraday.new(client_app.uri) do |conn|
-          conn.request(:authorization, "Bearer", -> {
- user_jwt(user, scopes: client_app.scopes, client_id: client_app.uid) })
-          conn.request(:json)
-          conn.response(:json)
-          conn.response(:raise_error)
-        end
+    #
+    # If scopes are specified (e.g. from an access token) these scopes are granted
+    # Otherwise the configured app scopes are used
+    def client_for(user, client_app, scopes: [])
+      scopes = scopes.empty? ? client_app.scopes : scopes
+
+      Faraday.new(client_app.uri) do |conn|
+        conn.request(
+          :authorization,
+          "Bearer",
+          -> { user_jwt(user, scopes: scopes, client_id: client_app.uid) }
+        )
+        conn.request(:json)
+        conn.response(:json)
+        conn.response(:raise_error)
       end
     end
 
-    # TODO: use the uri's generated by Version to dynamiclly pick the correct
-    # model and engine
-    def engine_client(user)
-      engine = OAuthApplication.find_by(uri: Settings.etengine.uri)
-      client_app_client(user, engine)
+    # Returns a Faraday client for a version of ETEngine
+    #
+    # If scopes are specified (e.g. from an access token) these scopes are granted
+    # Otherwise the configured app scopes are used
+    def engine_client(user, version_tag = Version::DEFAULT_TAG, scopes: [])
+      uri = Version.engine_url(version_tag)
+      engine = OAuthApplication.find_by(uri: uri)
+      client_for(user, engine, scopes: scopes)
     end
 
-    def model_client(user)
-      model = OAuthApplication.find_by(uri: Settings.etmodel.uri)
-      client_app_client(user, model)
+    # Returns a Faraday client for a version of ETModel
+    def model_client(user, version_tag = Version::DEFAULT_TAG)
+      uri = Version.model_url(version_tag)
+      model = OAuthApplication.find_by(uri: uri)
+      client_for(user, model)
     end
 
-
     # Checks if the token is in JWT format
     def jwt_format?(token)
       token.count(".") == 2
@@ -115,6 +125,6 @@ def verify_claims(decoded_token)
     end
 
     module_function :decode, :jwt_format?, :verify_claims, :signing_key_content, :user_jwt,
-      :signing_key, :model_client, :engine_client, :client_app_client
+      :signing_key, :model_client, :engine_client, :client_for
   end
 end
diff --git a/spec/controllers/api/v1/versions_controller_spec.rb b/spec/controllers/api/v1/versions_controller_spec.rb
index 5c63390..37ef1b9 100644
--- a/spec/controllers/api/v1/versions_controller_spec.rb
+++ b/spec/controllers/api/v1/versions_controller_spec.rb
@@ -19,8 +19,9 @@
 
       expect(parsed_response['versions']).to be_present
       expect(parsed_response['versions'].map { |v| v['tag'] }).to match_array(Version.tags)
-      expect(parsed_response['versions'].first).to have_key('url')
+      expect(parsed_response['versions'].first).to have_key('model_url')
       expect(parsed_response['versions'].first).to have_key('engine_url')
+      expect(parsed_response['versions'].first).to have_key('collections_url')
     end
   end
 end
diff --git a/spec/controllers/collections_controller_spec.rb b/spec/controllers/collections_controller_spec.rb
index a547e81..5ff043d 100644
--- a/spec/controllers/collections_controller_spec.rb
+++ b/spec/controllers/collections_controller_spec.rb
@@ -26,7 +26,7 @@
       end
 
       it 'redirects to the collection' do
-        post :create_transition, params: { collection: {saved_scenario_ids: scenario.id }}
+        post :create_transition, params: { collection: {saved_scenario_ids: scenario.id, version: Version.tags.last }}
 
         expect(response).to redirect_to(
           collection_path(Collection.last)
diff --git a/spec/requests/saved_scenarios_spec.rb b/spec/requests/saved_scenarios_spec.rb
index 5e1fff8..81d8cb5 100644
--- a/spec/requests/saved_scenarios_spec.rb
+++ b/spec/requests/saved_scenarios_spec.rb
@@ -38,7 +38,7 @@
   let(:admin) { FactoryBot.create(:admin) }
   let!(:admin_scenario) { FactoryBot.create(:saved_scenario, user: admin, id: 648696) }
 
-  before { allow(MyEtm::Auth).to receive(:client_app_client).and_return(client) }
+  before { allow(MyEtm::Auth).to receive(:client_for).and_return(client) }
 
   describe "GET /index" do
     before do