If you're running on Android, you can get this from the logcat output. You would need to have
adb installed, and adb logcat should have logs for this.
On iOS, XCode has a panel displaying logs, and the device ID is found there.
That said, you should still be able to get fill even if you didn't input the test device ID. Hopefully you're using a real ad unit ID. Once you have access to the logs, there should be an error reason why the ad didn't come back. You could actually also check the error from within Unity:
view1.AdLoaded += HandleAdLoaded;
view1.AdFailedToLoad += HandleAdFailedToLoad;
...
public void HandleAdLoaded()
{
print("HandleAdLoaded event received.");
}
public void HandleAdFailedToLoad(string message)
{
print("HandleFailedToReceiveAd event received with message: " + message);
}
to see what's going on.
Thanks,
Eric