Flutter admob ads not showing. Ad Failed to load : 3

Question

Admob's test ads or normal ads not showing on my flutter app. My ad requests return this error: 'Ad failed to load: 3'. I search this error code and found it:

The ad request was successful, but no ad was returned due to lack of ad inventory.
Constant Value: 3

But not only my ads, test ads also don't show. I use the google_mobile_ads package. Here's my codes:

main() at main.dart:

void main() {
   WidgetsFlutterBinding.ensureInitialized();
   MobileAds.instance.initialize();
   runApp(MyApp());
}

This variables at my main screen's state class (it is a stateful widget)

  BannerAd _ad;
  bool isLoaded = false;

The screen's initState function

void initState() {
    _ad = BannerAd(
        adUnitId: BannerAd.testAdUnitId,
        request: AdRequest(),
        size: AdSize.banner,
        listener: AdListener(
          onAdLoaded: (_) {
            print("loaded");
            setState(() {
              isLoaded = true;
            });
          },
          onAdFailedToLoad: (ad, error) {
            print("error: $error");
            ad.dispose();
          },
        ));
    _ad.load();
    super.initState();
  }

This condition is at bottom of main column

if (isLoaded)
    Container(
    width: _ad.size.width.toDouble(),
    height: _ad.size.height.toDouble(),
    child: AdWidget(ad: _ad),
    ),

Dispose method

  void dispose() {
    _ad?.dispose();
    super.dispose();
  }

And related part of the android/app/src/main/AndroidManifests.xml file

        <meta-data
            android:name="com.google.android.gms.ads.APPLICATION_ID"
            android:value="ca-app-pub-3940256099942544~3347511713"/>
    </application>

Answer 1

I experienced the same problem in my app since a few days. Seams to be a general problem, the example project provided by the package is failing too.

Issue is open #217