Hello,
Yes, I had good experience in terms notifications. I had manage notification using many sources like firebase, APN’s, One signal and many more. Here, you face error while sending notifications from server which mean that the p12 files or the key file that is p8 was uploaded a wrong one. You have to upload a correct p12 or p8 file to get notifications using fcm token. Here, there may be 2 from that there no notifications while application is open or the notifications is not cominin each state that is open app, app in background or terminate app. Let me know more about the actual issue you face. I will sort out it.
Thank you