How to keep android air app running in background

I created an audio app that runs fine when the screen is on. but when the screen is off the app will exit or crash (not sure what is really happening) after anywhere between 10 minutes and an hour. What's the trick to get it to continue the audio indefinitely after the screen is off or it is in the background. This used to not be a problem a couple of android versions ago. Testing this on Galaxy s9+. Thanks for your help.