I have a Nexus 5X running an unofficial Pie build (https://forum.xda-developers.com/nexus-5x/development/rom-android-source-project-t3827122)
VoLTE does not work (no incoming or outgoing calls), but data over LTE works. So the Jio4gVoice app should be able to receive calls (over data, meant for non-VoLTE phones). But the problem is that this app detects that the phone is VoLTE compatible and simply refuses to connect.
PS: The phone supports VoLTE, I've used it before, but this particular ROM doesn't.
I'm looking for a way to disable VoLTE so that the app can work.