iOS VoIP push notifications / PushKit is not working with Enhanced Notification Format

Question

I just tested VoIP push notifications with Simple Notification Format and Enhanced Notification Format and found out:

1. Using Simple Notification Format, our App can receive VoIP push notifications.

2. Using Enhanced Notification Format, our App can only receive regular push notifications.

Why does Enhanced Notification Format not work with VoIP push notifications / PushKit?

Answer 1

As stated in the apple docs, Simple and Enhanced Notification Format are deprecated:

New development should use the modern format to connect to APNs, as described in The Binary Interface and Notification Format.

PushKit / VoIP push notifications probably just work with the Simple Notification Format for legacy support reasons and for advanced functionality, the new notification format is used for PushKit rather than the deprecated one.