52104: Mismatched GCM/FCM sender ID

• GCM/FCM API Key provided is not allowed to send notifications to the registration token.

Make sure that you are using an API Key/Secret that is allowed to send notifications to your application.

• Add the Project number of the Google Developers Console/Firebase Console project that the API Key/Secret belongs to to the allowed sender IDs of your application
• Alternatively use an API Key/Secret from a project that is already allowed to send notifications to your application