I faced an issue while using the older version of FCM i.e 10.2.6, I was not getting the notification, I googled for this error and didn't get any results regarding this issue, so I posted this if someone faces this error.
Unknown intent action: com.google.firebase.MESSAGING_EVENT
update the gradle version to latest:
compile 'com.google.firebase:firebase-messaging:11.0.1
Now it started working
EDIT : This is not a Question, its Info if someone faces this issue