My VoIP app is installed on an iPad, but can't accept incoming calls by VoIP push.
But it works after I force-restart this iPad. I have some customers who encountered the same cases, fixed by force-restart too.
So my question is
Are these WiFi only iPads, or iPads with their cellular service turned off?
If so, the situation is easily explained. On an idle iPad the WiFi connection will at some point be turned off if no app is actively using it. In that state, the connection to APNs will also be obviously severed.
When you restart the iPad, the system will turn on WiFi again for a while, and the APNs connection will be re-established.
@Engineer The WIFI works well while the VoIP push doesn't work because my app works for other features, like sending/receiving messages via REST API. Just the VoIP push failed.
btw, you said "restart the iPad", is it means the "force-restart"? https://support.apple.com/en-sg/guide/iphone/iph8903c3ee6/ios