Admob LoadAdError 'message: No fill' on Test Devices - Flutter

Question

I have an app on google play which was previously build by native android and java but now I'm upgrading it to Flutter. I'm trying to add AdMob ads to the app. But it dose not load any test ad or real ad on the given Interstitial AD ID.

LoadAdError(code: 3, domain: com.google.android.gms.ads, message: No fill.,  
responseInfo: ResponseInfo(responseId: null, mediationAdapterClassName: , 
adapterResponses: [], loadedAdapterResponseInfo: null), responseExtras: {})

But when I try with default test AD ID ca-app-pub-3940256099942544/1033173712 it shows test ads.

My device Google AD ID's is already added to test devices in AdMob settings. I also have tried with different emulators and physical devices.

MobileAds.instance.openAdInspector((error) {
  debugPrint('Ad Inspector failed to load: $error');
});

I have also tried to load ad through AD Inspector but the Ad Inspector is not launching when I user the real Interstitial Ad ID and only launches when using the default AD ID.

Error for launching AD Inspector

Ad Inspector failed to load: null

Answer 1

Your ADCode is correct if you face error code "3" that means it's working As per this https://stackoverflow.com/a/33712905/18340828 not every time the ads unit has been filled