one of the best ways to implement push notifications via android or iOS is with FCM. But its been several years now, that this issue exists about applications not being able to receive notifications when apps are killed by teh user. This issue appears only on android. And the FCM team says it is due to vendors. I've tried a lot of "potential" solutions I found online to resolve this issue, but none of them actually worked. I have read several stack overflow questions about this topic and now I'm kind of desperate.
So please if someone knows how to implement this functionality just as what we see on whatsapp, Messenger and all the like, please help.