Does billing issue notification contain unique transaction ID or this transaction ID matches, for example, the last transaction ID in subscription renewal history?
I also didn't find info about:
- Can billing issue notification be produced multiple times? With different transaction ID or the same one?
All App Store Server Notifications contain the original_transaction_id and transaction_id but it may not be a new transaction as notifications are sent for events, which may or may not be actual transactions (ie: commonly transactions are buys/renewals/upgrades/refunds).
So for a subscription that has failed to renew, you would receive a notification for this event which will include the original_transaction_id of the subscription and their renewal info.
Lastly this notification is sent when the customers subscription has gone into the Billing Retry state - the state is important, not the individual payment authorization attempts as there is no action to take per attempt. A new event or state change is important, so when they fall they into this state, you would only receive a notification when their state changes: recover, cancel or the billing retry period has expired.