I did everything right: I linked the app with the firebase, but at the time of running the ad area it turns white. Now if I use the test unit id it works normally
MainActivity Code
AdView mAdView = (AdView) findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder().build();
mAdView.loadAd(adRequest);
Layout code
<com.google.android.gms.ads.AdView
android:id="@+id/adView"
android:layout_width="368dp"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_alignParentBottom="true"
ads:adSize="BANNER"
ads:adUnitId="@string/banner_ad_unit_id"
tools:layout_editor_absoluteY="8dp"
tools:layout_editor_absoluteX="8dp">
</com.google.android.gms.ads.AdView>
Strings
<resources>
<string name="app_name">My Application</string>
<string name="banner_ad_unit_id">ca-app-pub-
1770401303076452/1027518523</string>
</resources>