package com.example.myapplication;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import com.google.android.gms.ads.AdError;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.android.gms.ads.FullScreenContentCallback;
import com.google.android.gms.ads.LoadAdError;
import com.google.android.gms.ads.MobileAds;
import com.google.android.gms.ads.initialization.InitializationStatus;
import com.google.android.gms.ads.initialization.OnInitializationCompleteListener;
import com.google.android.gms.ads.interstitial.InterstitialAd;
import com.google.android.gms.ads.interstitial.InterstitialAdLoadCallback;

public class MainActivity extends AppCompatActivity {

    private InterstitialAd mInterstitialAd;
    private Button mInterstitialButton;
    private AdRequest adRequest;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MobileAds.initialize(this, new OnInitializationCompleteListener() {
            @Override
            public void onInitializationComplete(InitializationStatus initializationStatus) {
            }
        });

        final boolean[] volt = {false};

        AdView mAdView = findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        Button bannerbutton = findViewById(R.id.BannerbtnAds);
                bannerbutton.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        if (!volt[0]) {
                            mAdView.loadAd(adRequest);
                            mAdView.setVisibility(View.VISIBLE);
                            volt[0] = true;
                        } else {
                            mAdView.setVisibility(View.GONE);
                            volt[0] = false;
                        }

                    }
                });

        InterstitialAd.load(this,"ca-app-pub-3940256099942544/1033173712", adRequest,
                new InterstitialAdLoadCallback() {
                    @Override
                    public void onAdLoaded(@NonNull InterstitialAd interstitialAd) {
                        // The mInterstitialAd reference will be null until
                        // an ad is loaded.
                        mInterstitialAd = interstitialAd;
                    }

                    @Override
                    public void onAdFailedToLoad(@NonNull LoadAdError loadAdError) {
                        // Handle the error
                        mInterstitialAd = null;
                    }
                });


        Button button = findViewById(R.id.IntbtnAds);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if (mInterstitialAd != null) {
                    mInterstitialAd.show(MainActivity.this);
                } else {
                    Log.d("TAG", "The interstitial ad wasn't ready yet.");
                }
            }
        });


    }
}

The interstitial ad shows only once, after that: The interstitial ad has been shown.

How can I fix it?