title: Admob Ads not showing in android application
body: <p>I created an account at Admob since a month, and i added payment method since 2 days ago.
  a test device showing ads successfully. but other devices don't show any thing with error code:3</p>
  
  <blockquote>
    <p>Ads: Ad failed to load : 3</p>
  </blockquote>
  
  <pre><code>public class MainActivity extends AppCompatActivity implements RewardedVideoAdListener {
      private AdView adView;
      private Button onePlayer, twoPlayer, exit;
      private InterstitialAd mInterstitialAd;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          MobileAds.initialize(this, getString(R.string.app_id));
          MobileAds.initialize(this, initializationStatus -&gt; {
  
          });
          mInterstitialAd = new InterstitialAd(this);
          mInterstitialAd.setAdUnitId(getString(R.string.instruction));
          mInterstitialAd.loadAd(new AdRequest.Builder().addTestDevice("my-device-id").build());
          mInterstitialAd.setAdListener(InterstitialListener);
          adView = findViewById(R.id.adView);
          adView.loadAd(new AdRequest.Builder().addTestDevice("my-device-id").build());
          adView.setAdListener(adListener);
     }
  }
  
  </code></pre>
  
  <p>and i created a listener for InterstitialAd</p>
  
  <pre><code>private AdListener InterstitialListener = new AdListener() {
          @Override
          public void onAdLoaded() {
              // Code to be executed when an ad finishes loading.
              mInterstitialAd.show();
          }
  
          @Override
          public void onAdFailedToLoad(int errorCode) {
              // Code to be executed when an ad request fails.
              Toast.makeText(getApplicationContext(), "errorCode " + errorCode + "", Toast.LENGTH_LONG).show();
          }
  
          @Override
          public void onAdOpened() {
              // Code to be executed when the ad is displayed.
          }
  
          @Override
          public void onAdClicked() {
              // Code to be executed when the user clicks on an ad.
          }
  
          @Override
          public void onAdLeftApplication() {
              // Code to be executed when the user has left the app.
          }
  
          @Override
          public void onAdClosed() {
              // Code to be executed when the interstitial ad is closed.
          }
      };
  </code></pre>
  
  <p>and this is banner xml:</p>
  
  <pre><code>&lt;com.google.android.gms.ads.AdView
      xmlns:ads="http://schemas.android.com/apk/res-auto"
      android:id="@+id/adView"
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      ads:adSize="BANNER"
      ads:adUnitId="@string/banner"&gt;
  &lt;/com.google.android.gms.ads.AdView&gt;
  </code></pre>
  
  <p>Note: the app doesn't uploaded to store yet!</p>
  
  <p>how can i fix this problem?</p>