Kickstarting Ads Kit by integrating Interstitial Ads in Application (Kotlin)

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
<!--check wifi state--> 
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

-keep class com.huawei.openalliance.ad.** { *; }
-keep class com.huawei.hms.ads.** { *; }

Create an InterstitialAd object and use the setAdId() method of the InterstitialAd class to set a test ad unit ID

private var interstitialAd: InterstitialAd? = null
var nextPageBtn: Button? = null
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
nextPageBtn = findViewById(R.id.btTrans)
  interstitialAd = InterstitialAd(this)
        interstitialAd.setAdId(adId)
        interstitialAd.setAdListener(adListener)
}

Call the loadAd() method of the InterstitialAd object to load an ad. 
private fun loadInterstitialAd() {
    ...
    // Load an interstitial ad.
    val adParam = AdParam.Builder().build()
    interstitialAd!!.loadAd(adParam)
    ...
}

Call the isLoaded() method to check whether an ad has been loaded. If the ad has been loaded, call the show(Activity activity) method of the InterstitialAd object to display the ad.
private fun showInterstitial() {
        // Display an interstitial ad.
        if (interstitialAd != null && interstitialAd.isLoaded()) {
            interstitialAd.show()
        } else {
            startActivity(Intent(this@MainActivity, pin::class.java))
        }
    }

Call the setAdListener(AdListener adListener) method of the InterstitialAd class to add the ad event listener AdListener for the InterstitialAd object, and implement the methods in AdListener to listen to ad events.
fun adEvent() {
    adListener = object : AdListener() {
        fun onAdLoaded() {
            // Called when an ad is loaded successfully.
            super.onAdLoaded()
            Toast.makeText(this@MainActivity, "Ad loaded", Toast.LENGTH_SHORT).show()
            // Display an interstitial ad.
            showInterstitial()
        }

        fun onAdFailed(errorCode: Int) {
            // Called when an ad fails to be loaded.
            Toast.makeText(
                this@MainActivity, "Ad load failed with error code: $errorCode",
                Toast.LENGTH_SHORT
            ).show()
            Log.d(
                TAG,
                "Ad load failed with error code: $errorCode"
            )
            startActivity(Intent(this@MainActivity, pin::class.java))
        }

        fun onAdClosed() {
            // Called when an ad is closed
            super.onAdClosed()
            Log.d(TAG, "onAdClosed")
            startActivity(Intent(this@MainActivity, pin::class.java))
        }

        fun onAdClicked() {
            // Called when an ad is clicked.
            Log.d(TAG, "onAdClicked")
            super.onAdClicked()
            adListener.onAdClosed()
        }

        fun onAdOpened() {
// Called when an ad is opened.
            Log.d(TAG, "onAdOpened")
            super.onAdOpened()
        }

        fun onAdLeave() {
            // Called when an ad leaves an app.
            ...
        }
        fun onAdLeave() {
            // Called when an ad leaves an app.
            ...
        }
    }
}
Activity_mail.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
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"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    tools:context=".MainActivity"
    android:id="@+id/activity_main"
    android:background="@color/purple_200">

    <Button
        android:id="@+id/btTrans"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/click_to_start_transaction"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        tools:layout_editor_absoluteY="327dp" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/welcome_to_world_s_best_bank"
        android:textSize="20dp" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:srcCompat="@drawable/hello" />
</RelativeLayout>