FCM getting MismatchSenderId

Question

I have an application that uses Google FCM for sending push notifications.

When i send a push notification to a group of users, i get a response of MismatchSenderId for some of them. Even though, all users have the exact same application. How can some of the users get a success response and others get a MismatchSenderId?

I have researched a lot and made sure I have added all prerequisites that FCM needs.

Any suggestions?

EDIT:

Sample response:

{"multicast_id":5340432438815499122,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"MismatchSenderId"}]}

EDIT 2:

Here is the server side sending code (PHP):

$fields = array
(
  'to' => $token,
  'data' => $data
);

$headers = array
(
  'Authorization: key=AIza**************************',
  'Content-Type: application/json'
);

$ch = curl_init();
curl_setopt( $ch,CURLOPT_URL, 'https://fcm.googleapis.com/fcm/send' );
curl_setopt( $ch,CURLOPT_POST, true );
curl_setopt( $ch,CURLOPT_HTTPHEADER, $headers );
curl_setopt( $ch,CURLOPT_RETURNTRANSFER, true );
curl_setopt( $ch,CURLOPT_SSL_VERIFYPEER, true );
curl_setopt( $ch,CURLOPT_POSTFIELDS, json_encode($fields) );
curl_exec( $ch );
curl_close( $ch );

UPDATE:

It seems that the issue has been resolved with the SDK updates. I am using now the latest com.google.firebase:firebase-messaging:9.6.1, I don't get "MismatchSenderId" anymore.

Answer 1

THIS WORKED FOR ME:

• CHECK WHICH FIREBASE PROJECT YOUR CURRENT ANDROID PROJECT IS LINKED TO AND USE Server Key FROM THAT PROJECT.

I was using Server key from a different firebase project(say Project 2). I used the same server key as linked with my android project(Say Project 1) and it worked. In my experience, using one firebase app for one entire android project seemed to fix the problem.