FCM notification issue

Hi,

I'm flutter developer, I want to build chat & video calling app.
My app almost done, but face couple of issue about FCM notification.

Sometimes, FCM silent notification not comming, I'm using flutter_callkit_incoming.

• App open Foreground (Working fine)
• App Background (Working maximum time)
• App Terminated (App not working)

Any one help me, please.

Advance thanks