Why do I get “MismatchSenderId” from GCM server side?

Did your server use the new registration ID returned by the GCM server to your app? I had this problem, if trying to send a message to registration IDs that are given out by the old C2DM server.

And also double check the Sender ID and API_KEY, they must match or else you will get that MismatchSenderId error. In the Google API Console, look at the URL of your project:

https://code.google.com/apis/console/#project:xxxxxxxxxxx

The xxxxxxxxx is the project ID, which is the sender ID.

And make sure the API Key belongs to 'Key for server apps (with IP locking)'

Mismatch happens when you don't use the numeric ID. Project ID IS NOT SENDER ID!! It took me 9 hours to figure this out. For all the confusion created by google, check the following link to get numeric id.

https://console.cloud.google.com

instead of

https://console.developers.google.com

Hope it helps!!

Update:- Things have changed again. Now the sender id is with firebase.

Go to https://console.firebase.google.com and select your project. Under settings -> cloud messaging, you can find the sender id.

And it works!

Please run below script in your terminal

curl -X POST \
-H "Authorization: key=  write here api_key" \
-H "Content-Type: application/json" \
-d '{ 
"registration_ids": [ 
"write here reg_id generated by gcm"
], 
"data": { 
"message": "Manual push notification from Rajkumar"
},
"priority": "high"
}' \
https://android.googleapis.com/gcm/send

it will give the message if it is succeeded or failed

I encountered the same issue recently and I tried different values for "gcm_sender_id" based on the project ID. However, the "gcm_sender_id" value must be set to the "Project Number".

You can find this value under: Menu > IAM & Admin > Settings.

See screenshot: GCM Project Number

InstanceID.getInstance(getApplicationContext()).getToken(authorizedEntity,scope)

authorizedEntity is the project number of the server

Your android app needs to correct 12-digit number id (aka GCM Project Number). If this 12-digit number is incorrect, then you will also get this error.

This 12-digit number is found in your Google Play Console under your specific app, 'Service & API' -> 'LINKED SENDER IDS'

This happens when the Server key and Sender ID parameters HTTP request do not match each other. Basically both server ID and Server key must belong to the same firebase project. Please refer to the below image. In case of mixing these parameters from deferent Firebase projects will cause error MismatchSenderId

Use sender ID & API Key generated here: http://developers.google.com instead (browse for Google Cloud Messaging first and follow the instruction).

If use for native Android, check your AndroidMaifest.xml file:

<meta-data
        android:name="onesignal_google_project_number"
        android:value="str:1234567890" />  
  <!--             its is correct. -->

instead

   <meta-data
        android:name="onesignal_google_project_number"
        android:value="@string/google_project_number" />

Hope it helps!!