title: AdMob RewardedVideoAd.loadAd always returns "failed to load ads, error code: 0"
body: <p>I'm using firebase-ads:9.2.0 with API level 24.</p>
  
  <p>And unity-ads aar module is imported by adding compile(name:'unity-ads', ext:'aar') to my build.gradle.</p>
  
  <p>Everything goes fine if I choose to use UnityAds API directly.</p>
  
  <p>But when I try to integrate unity-ads with AdMob like this:</p>
  
  <pre><code>    mRewardedVideoAd = MobileAds.getRewardedVideoAdInstance( this );
  
      mRewardedVideoAd.setRewardedVideoAdListener(new RewardedVideoAdListener() {
          @Override
          public void onRewardedVideoAdLoaded() {
              logger.debug("onRewardedVideoAdLoaded");
          }
  
          @Override
          public void onRewardedVideoAdOpened() {
              logger.debug("onRewardedVideoAdOpened");
          }
  
          @Override
          public void onRewardedVideoStarted() {
              logger.debug("onRewardedVideoStarted");
          }
  
          @Override
          public void onRewardedVideoAdClosed() {
              logger.debug("onRewardedVideoAdClosed");
          }
  
          @Override
          public void onRewarded(RewardItem rewardItem) {
              logger.debug("onRewarded");
          }
  
          @Override
          public void onRewardedVideoAdLeftApplication() {
              logger.debug("onRewardedVideoAdLeftApplication");
          }
  
          @Override
          public void onRewardedVideoAdFailedToLoad(int i) {
              Toast.makeText( 
                  getApplicationContext(), 
                  "onRewardedVideoAdFailedToLoad", 
                  Toast.LENGTH_SHORT ).show();
          }
      });
  
      AdRequest adRewardRequest = new AdRequest.Builder()
          .addTestDevice("E921B48960E16DA3ABD13C4AFB7052A4")
          .build();
  
      mRewardedVideoAd.loadAd( 
          getResources().getString(R.string.reward_ad_unit_id), 
          adRewardRequest );
  </code></pre>
  
  <p>It always returns</p>
  
  <blockquote>
    <p>There was a problem getting an ad response. ErrorCode: 0<br>
    Failed to load ad: 0.</p>
  </blockquote>
  
  <p>Is there anything I did it in the wrong way?</p>
  
  <p>Or I just missed some steps?</p>
  
  <p>Here is my AdMob page screenshot:</p>
  
  <p><a href="https://i.stack.imgur.com/KVSI1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/KVSI1.png" alt="AdMob page"></a></p>