奖励视频广告无法加载

Question

我创建了一个带有奖励视频广告的应用。当我点击按钮时，广告没有被加载。我曾尝试测试广告单元ID和我的admob ID，但均无济于事。每当我点击按钮时，它就会显示“广告服务器未填充。无法加载广告：3” 我不知道该怎么办。

MobileAds.initialize(getApplicationContext(),"ca-app-pub-4786107620829013~6803627405");
    mad =   MobileAds.getRewardedVideoAdInstance(this);
    mad.setRewardedVideoAdListener(this);
    mad.loadAd("ca-app-pub-xxxxxxxxxxx", new AdRequest.Builder().build());

public void Clicked(View view) {
    if (mad.isLoaded())
    {
        mad.show();
    }

}

@Override
public void onRewardedVideoAdLoaded() {
    Toast.makeText(this, "Video loaded", Toast.LENGTH_SHORT).show();
}

@Override
public void onRewardedVideoAdOpened() {
    Toast.makeText(this, "Video Opened", Toast.LENGTH_SHORT).show();
}

@Override
public void onRewardedVideoStarted() {
    Toast.makeText(this, "Video Started", Toast.LENGTH_SHORT).show();

}

@Override
public void onRewardedVideoAdClosed() {

     }

@Override
public void onRewarded(RewardItem rewardItem) {

  }

@Override
public void onRewardedVideoAdLeftApplication() {

}

@Override
public void onRewardedVideoAdFailedToLoad(int i) {
    Toast.makeText(this, "Fail", Toast.LENGTH_SHORT).show();
}

@Override
public void onRewardedVideoCompleted() {
    Toast.makeText(this, "Complete Video", Toast.LENGTH_SHORT).show();
}