"Your app must have an active audio session before entering the background. If your app’s audio session is deactivated when the app enters the background your app will be suspended, because as far as the system knows, your app is no longer playing audio.
I had that issue when I was trying to get my app published initially. I had to submit a ticket to adalo, and they helped resolve the issue. It may be something they have to fix on the backend.
It’s been a while, so I can’t quite remember the fix. (I used the the Adalo Audio Player component and that’s what I still have in my app.) I’ll check back through my emails and see if I can get anything more specific. Meanwhile, I would suggest submitting a ticket if you haven’t already.