title: FCM getting MismatchSenderId
body: <p>I have an application that uses Google FCM for sending push notifications.</p>
  
  <p>When i send a push notification to a group of users, i get a response of <code>MismatchSenderId</code> 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?</p>
  
  <p>I have researched a lot and made sure I have added all prerequisites that FCM needs.</p>
  
  <p>Any suggestions?</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>Sample response:</p>
  
  <pre><code>{"multicast_id":5340432438815499122,"success":0,"failure":1,"canonical_ids":0,"results":[{"error":"MismatchSenderId"}]}
  </code></pre>
  
  <p><strong>EDIT 2:</strong></p>
  
  <p>Here is the server side sending code (PHP):</p>
  
  <pre><code>$fields = array
  (
    'to' =&gt; $token,
    'data' =&gt; $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 );
  </code></pre>
  
  <p><strong>UPDATE:</strong></p>
  
  <p>It seems that the issue has been resolved with the SDK updates. I am using now the latest <code>com.google.firebase:firebase-messaging:9.6.1</code>, I don't get "MismatchSenderId" anymore.</p>