It seems you’re encountering a 401 Unauthorized error when trying to use FCM V1 with Azure Notification Hub. Verify that the API Key you provided in Azure Notification Hub is a Server Key. If it’s not, you might need to create a new one specifically for server-side use. Make sure you’ve correctly configured the FCM V1 credentials (private key, client ID, etc.) in Azure Notification Hub.
Ensure that the Authorization rules are correctly set up for your Notification Hub. If they are missing, add the necessary rules in the Azure portal. Copy the corresponding connection string from the portal and use it with the Notification Hub Android API. Use the Azure portal’s “Test Send” feature to verify if notifications are working correctly. This will help you identify any issues related to your configuration.