I’m not familiar with btrbk specifically, but my backups all send a ping to healthchecks.io when they start and when they finish. healthchecks.io works by getting a simple curl request, similar to ntfy, but if that request doesn’t happen after a certain amount of time (or if you do a start request and a succeed/fail request and the job is taking too long) then it will notify you. It can use ntfy for notifications, but it can also send emails or use any of a number other services.