No notification when app goes to background or is closed (Flutter + Agora)

I am using Agora in a Flutter app.

When the user is in a call and:
1. The app goes to background, or
2. The user closes the app (swipe away)

Then:
1. Nothing shows on the screen
2. No “ongoing call” notification appears
3. The other side cannot hear any audio
4. I am not sure if the call is still connected or not

Everything works fine while the app is open, but after closing or backgrounding the app, audio stops and the call becomes inactive.

Kindly help to understand how to keep the call active and working when the app is backgrounded or closed.