I just copy Answer from same question here becuase this page is first result in google: Get all subscribed topics from firebase cloud messaging
https://iid.googleapis.com/iid/info/<TOKEN>?details=true
Content-Type:application/json
Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA
TOKEN in url : FirebaseInstanceId.getInstance().getToken();
key : can be found in [firebase console][1]: Your project -> settings -> Project settings -> Cloud messaging -> Server Key