Рекламные вставки Admob не отображаются при нажатии кнопки Android

Question

Я пытаюсь настроить Interstitial. но это не работаетПожалуйста, посмотрите на код и сообщите мне, если я где-то совершаю ошибку.

@Override
protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    btn = findViewById( R.id.image_button_download );

    mAdView = findViewById(R.id.adView);
    AdRequest adRequest = new AdRequest.Builder().build();
    mAdView.loadAd(adRequest);

    MobileAds.initialize(this, new OnInitializationCompleteListener() {
        @Override
        public void onInitializationComplete(InitializationStatus initializationStatus) {}
    });

    mInterstitialAd = new InterstitialAd(this);
    mInterstitialAd.setAdUnitId("ca-app-pub-3940256099942544/1033173712");
    mInterstitialAd.loadAd(new AdRequest.Builder().build());
    // Create ad request
    adRequest = new AdRequest.Builder().build();
    // Attempt loading ad for interstitial
    mInterstitialAd.loadAd(adRequest);
    // Create and set AdListener for interstitial
    mInterstitialAd.setAdListener(new AdListener() {
        // Listen for when user closes ad
        public void onAdClosed() {
            // When user closes ad end this activity (go back to first activity)
            finish();
        }
    });

    btn.setOnClickListener(new View.OnClickListener() {
        // Listen for when user presses button
        public void onClick(View v) {
            // If a interstitial is ready, show it
            if (mInterstitialAd.isLoaded()) {
                mInterstitialAd.show();
            } else {
                Log.d("TAG", "The interstitial wasn't loaded yet.");
            }
        }
    });

Объявлена ​​кнопка:

public class MainActivity extends AppCompatActivity
{
    private static final String TAG = MainActivity.class.getSimpleName();

    public static final String PREF_ACCOUNT_NAME = "accountName";

    static final int REQUEST_ACCOUNT_PICKER = 1000;
    static final int REQUEST_PERMISSION_GET_ACCOUNTS = 1003;
    private Button btn;
    private InterstitialAd mInterstitialAd;

Activity_ Main Layout:

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:ads="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.mediaplus.youtubemp3downloader.ui.MainActivity">


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.google.android.material.appbar.AppBarLayout
            android:id="@+id/appBarLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
            <include layout="@layout/toolbar_main"/>
            <include layout="@layout/tablayout_main"/>

            <com.google.android.gms.ads.AdView
                android:id="@+id/adView"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                ads:adSize="BANNER"
                ads:adUnitId="ca-app-pub-3940256099942544/6300978111">
            </com.google.android.gms.ads.AdView>

        </com.google.android.material.appbar.AppBarLayout>

        <androidx.viewpager.widget.ViewPager
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_above="@+id/controls_container"
            android:layout_below="@+id/appBarLayout"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

        </androidx.viewpager.widget.ViewPager>

        <androidx.cardview.widget.CardView
            android:id="@+id/controls_container"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignWithParentIfMissing="true">

            <fragment
                android:id="@+id/fragment_playback_controls"
                android:name="com.mediaplus.youtubemp3downloader.ui.fragments.PlaybackControlsFragment"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_alignParentBottom="true"
                tools:layout="@layout/fragment_playback_controls"/>

        </androidx.cardview.widget.CardView>

    </RelativeLayout>



</androidx.coordinatorlayout.widget.CoordinatorLayout>