diff --git a/openapi-spec/api-v1.yaml b/openapi-spec/api-v1.yaml
index 1d439afa..19b5bbc7 100644
--- a/openapi-spec/api-v1.yaml
+++ b/openapi-spec/api-v1.yaml
@@ -1029,6 +1029,11 @@ components:
                         - `play_store`: The product was purchased through the Google Play Store.
                         - `amazon`: The product was purchased through the Amazon Appstore.
                         - `stripe`: The product was purchased through Stripe.
+                    store_transaction_id:
+                      type: string
+                      example: GPA.3314-8787-2119-77742
+                      description: |
+                        Identifier of the purchase in the store's API.
             original_app_user_id:
               type: string
               example: XXX-XXXXX-XXXXX-XX
@@ -1176,6 +1181,7 @@ components:
                 is_sandbox: true
                 purchase_date: "2019-04-05T21:52:45Z"
                 store: app_store
+                store_transaction_id: "GPA.3314-8787-2119-77742"
           original_app_user_id: XXX-XXXXX-XXXXX-XX
           original_application_version: "1.0"
           original_purchase_date: "2019-01-30T23:54:10Z"