Mismatched Users is thrown when Google returns a MismatchSenderId error. This is because some users' FCM registration tokens are tied to a Google Server API key that no longer matches their current project's Google Server API key.

This generally occurs if...

1. Your Firebase project was deleted
2. You changed the Firebase Project ID and/or Firebase Server API Key
3. You are still using the GCM keys and need to switch over to FCM, see the last section of this page.

We recommend using Firebase Cloud Messaging API (V1), as Cloud Messaging API (Legacy) will be deprecated by Google in June 2024. Learn how to update your credentials.

If you're using FCM V1, you can update the Service Account JSON File in your dashboard settings, which will automatically detect the associated Project ID. Beware that using a file associated with a different Project ID will make all current subscriptions invalid and unable receive push notifications until the user opens the app on the device again.

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Android Messaging Warning

Keep in mind that changing your Project ID will cause all devices that subscribed to the old project number to become invalid and will not be able to receive notifications until they re-open the app. Upon which, our SDK will update them to the new project number. No app update required.

Update Cloud Messaging API to Firebase Cloud Messaging API

If you are updating to FCM, you can import the GCM keys into Firebase which will keep the same Project ID but will make it FCM.

Within https://console.firebase.google.com press "Add project" and select your existing Google project to import it to FCM.

You will see your GCM projects listed when you click the down arrow like this: https://i.imgur.com/ztLmdYJ.png

Your Sender ID should stay the same. Your Server API key may change. Follow the steps to change Android FCM Keys.