Push to Talk IOS App

We have an existing app developed in react native like zello push to talk. we want to play the audio message automatically without any user interaction when the app is in background or killed. Whenever any user sending real time audio message, I am sending a push notification to ios app and after receiving notification we are invoking a function which establishes socket connection with the webrtc server and then join in the room in which webrtc audio broadcasting is happening. Now we have checked that socket is connected and also joining in room successfully done after receiving push notification when app is in background. But there we could not hear any audio and received following error message.

AURemoteIO.cpp:1668 AUIOClient_StartIO failed (561145187)

Then we have set AVAudioSessionCategoryPlayback and that error gone. But this time also did not hear any audio sound. The app is working fine when it is in foreground. We are looking for experienced voip developer who can implement this part for us.