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We are developing a mobile app with in-app purchases. We plan to offer one-time purchases and subscriptions. In order to support multiple platforms (iOS and others) we plan to track subscriptions via server-to-server notifications and update client licenses accordingly. Now we are struggling to match server notifications to receipts in the database. We have to support iOS14, so we can't use the appAccountToken field. We have the following questions: Is original_transaction_id unique a) globally (across all app store user accounts) ? b) in the context of a user account ? c) in the context of a subscription group? Is original_transaction_id + subscription_group_identifier unique a) globally (across all app store user accounts) ? b) in the context of an user account ? Can an original_transaction_id change? If an original_transaction_id changed, how can I reference the INITIAL_BUY receipt? Thank you for your help!