Following this thread, we have defined a V1 Sandbox URL and a V1 Production URL. This works just fine and has helped us a lot in testing. We appreciate it very much! But with this change, we have started receiving "RENEWAL" notifications in some new Sandbox purchases. According to the documentation, this notification type has been deprecated and since March 2021 should not be sent. The purchases which triggered these notifications are all from this year. Are we missing something? Or is this a bug?

With the recent changes we've stopped receiving App Store Server Notifications V1 and we can only receive the V2 Notifications. Does anyone know how to solve this?