Add full params on first addons purchase

ee/app/services/subscriptions/create_service.rb

@@ -71,10 +71,7 @@ module Subscriptions
     end
 
     def create_subscription(customer_data)
-      # When purchasing an add on, we don't want to send create_subscription_params
-      # in order to avoid amending the main product. Note that this will go away
-      # when fully transitioning the flow to GraphQL
-      create_params = add_on? ? create_addon_params : create_subscription_params
+      create_params = send_create_addon_params? ? create_addon_params : create_subscription_params
       billing_email, token = customer_data.values_at(:email, :authentication_token)
 
       client.create_subscription(create_params, billing_email, token)
@@ -112,6 +109,14 @@ module Subscriptions
       Gitlab::Utils.to_boolean(subscription_params[:is_addon], default: false)
     end
 
+    def send_create_addon_params?
+      # We don't want to send create_subscription_params when purchasing addon
+      # in order to avoid amending the main product. The only exception to it
+      # is when we don't have an active subscription for a group purchasing addon.
+      # Note that this will go away when fully transitioning the flow to GraphQL
+      add_on? && subscription_params[:active_subscription].present?
+    end
+
     def country_code(country)
       World.alpha3_from_alpha2(country)
     end

ee/spec/fixtures/create_service_params.json

-[
-  {
+{
+  "subscription_params": {
     "customer": {
       "provider": "gitlab",
       "uid": 111,
@@ -35,7 +35,7 @@
       "source": "some_source"
     }
   },
-  {
+  "addon_with_active_sub": {
     "customer": {
       "provider": "gitlab",
       "uid": 111,
@@ -67,5 +67,41 @@
       "preview": "false",
       "source": "some_source"
     }
+  },
+  "addon_without_active_sub": {
+    "customer": {
+      "provider": "gitlab",
+      "uid": 111,
+      "credentials": {
+        "token": "foo_token"
+      },
+      "customer": {
+        "country": "NLD",
+        "address_1": "Address line 1",
+        "address_2": "Address line 2",
+        "city": "City",
+        "state": "State",
+        "zip_code": "Zip code",
+        "company": "My organization"
+      },
+      "info": {
+        "first_name": "First name",
+        "last_name": "Last name",
+        "email": "first.last@gitlab.com"
+      }
+    },
+    "subscription": {
+      "plan_id": "Add-on Plan ID",
+      "payment_method_id": "Payment method ID",
+      "products": {
+        "main": {
+          "quantity": 111
+        }
+      },
+      "gl_namespace_id": 222,
+      "gl_namespace_name": "Group name",
+      "preview": "false",
+      "source": "some_source"
+    }
   }
-]
+}
\ No newline at end of file

ee/spec/services/subscriptions/create_service_spec.rb

@@ -32,7 +32,7 @@ RSpec.describe Subscriptions::CreateService do
 
   let_it_be(:customer_email) { 'first.last@gitlab.com' }
   let_it_be(:client) { Gitlab::SubscriptionPortal::Client }
-  let_it_be(:create_service_params) { Gitlab::Json.parse(fixture_file('create_service_params.json', dir: 'ee'))[0].deep_symbolize_keys }
+  let_it_be(:create_service_params) { Gitlab::Json.parse(fixture_file('create_service_params.json', dir: 'ee'))["subscription_params"].deep_symbolize_keys }
 
   describe '#execute' do
     before do
@@ -127,7 +127,6 @@ RSpec.describe Subscriptions::CreateService do
         let_it_be(:subscription_params) do
           {
             is_addon: true,
-            active_subscription: 'A-000000',
             plan_id: 'Add-on Plan ID',
             payment_method_id: 'Payment method ID',
             quantity: 111,
@@ -135,12 +134,28 @@ RSpec.describe Subscriptions::CreateService do
           }
         end
 
-        it 'passes the correct parameters for creating a subscription' do
-          create_service_addon_params = Gitlab::Json.parse(fixture_file('create_service_params.json', dir: 'ee'))[1].deep_symbolize_keys
+        context 'without active subscription' do
+          it 'passes the correct parameters for creating a subscription' do
+            create_service_addon_params = Gitlab::Json.parse(fixture_file('create_service_params.json', dir: 'ee'))["addon_without_active_sub"].deep_symbolize_keys
 
-          expect(client).to receive(:create_subscription).with(create_service_addon_params[:subscription], customer_email, 'token')
+            expect(client).to receive(:create_subscription).with(create_service_addon_params[:subscription], customer_email, 'token')
 
-          execute
+            execute
+          end
+        end
+
+        context 'with active subscription' do
+          before do
+            subscription_params[:active_subscription] = 'A-000000'
+          end
+
+          it 'passes the correct parameters for creating a subscription' do
+            create_service_addon_params = Gitlab::Json.parse(fixture_file('create_service_params.json', dir: 'ee'))["addon_with_active_sub"].deep_symbolize_keys
+
+            expect(client).to receive(:create_subscription).with(create_service_addon_params[:subscription], customer_email, 'token')
+
+            execute
+          end
         end
       end