Hello: The App Store provides https://developer.apple.com/help/app-store-connect/configure-in-app-purchase-settings/enter-server-urls-for-app-store-server-notifications When the server interfaces with this interface, it is found that the specific user account cannot be found. How should I know which user initiated the subscription, or which user automatically subscribed during automatic renewal? Do you have a user account or ID? I hope to receive your complete answer as soon as possible. Best wishes.
Check out the appAccountToken, found in the transaction information included in notifications: https://developer.apple.com/documentation/appstoreservernotifications/appaccounttoken
Additionally for auto-renewable subscriptions, the originalTransactionId can be used as a consistent identifier of the sub across renewals (and notifications). https://developer.apple.com/documentation/appstoreservernotifications/originaltransactionid