Invalid Google Credentials is thrown when your Google Server API Key is entered incorrectly. This error can also happen to keys that were generated using the Google Cloud Console due to a bug with Google's systems.
Follow this guide to generate a new Server API Key: https://documentation.onesignal.com/docs/generate-a-google-server-api-key.
Make sure you are generating an API key for the correct Google Project.
Contact support with your correct Google Server API key, GCM/FCM number, and APP ID to verify your account.
Updated about 4 years ago