If a webhook notification is not delivered successfully, Banked will attempt to re-deliver it 25 times, using exponential backoff. The last retry will happen about 21 days after the initial attempt.
Re-delivery is triggered by responses with HTTP statuses between 400 and 599 (except 410), as well as by timeouts or DNS lookup failures.
Although unlikely to happen, it's important you account for this retry logic in your implementation and don't double-count the notifications in case a false negative response is returned to Banked.