This is how to play audio on background (Ionic v4 + android 10)

First install:

Then we need to use backgroundMode event listening for activate to resume the audio whenever the app goes to background, you will notice a tiny micropause, but that’s it!

this.nativeAudio.play("audio1"),() => console.log('audio1 is done playing'));

this.backgroundMode.enable();
this.backgroundMode.on("activate").subscribe(()=>{
   this.nativeAudio.play("audio1");  
});