Sending FCM notification with Fids Return NotRegistered

[FabienBounoir]

Environment

• FirebaseAdmin: 3.6.0
• .NET: (your version)
• Platform: iOS
• FCM HTTP v1 (through Firebase Admin SDK)

Description

I'm trying to migrate from registration tokens to FIDs as recommended by the SDK.

When sending a notification to an Apple device using the Fid property of Message, the Admin SDK always returns a FirebaseMessagingException with the error NotRegistered.

However, using the exact same FID from the Firebase Console ("Send test message"), the notification is delivered successfully to the device.

This suggests either:

• the .NET Admin SDK is not sending the request correctly when using Message.Fid, or
• there is a backend/API discrepancy between the Admin SDK and the Firebase Console.

Code

var message = new Message
{
    Fid = fid,
    Notification = new Notification
    {
        Title = "Test",
        Body = "Hello"
    }
};

await FirebaseMessaging.DefaultInstance.SendAsync(message);