AdMob Interstitial Ads of andorid

 import android.annotation.SuppressLint
 import android.os.Bundle
 import androidx.appcompat.app.AppCompatActivity 
 import com.google.android.gms.ads.AdListener
 import com.google.android.gms.ads.AdRequest
 import com.google.android.gms.ads.InterstitialAd
 import com.google.android.gms.ads.MobileAds


 class MainActivity : AppCompatActivity() {
     lateinit var interstitialAd: InterstitialAd
     @SuppressLint("VisibleForTests")
     lateinit var adRequest: AdRequest
     @SuppressLint("MissingInflatedId")
     override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)

         MobileAds.initialize(this)
         adRequest = AdRequest.Builder().build()
         interstitialAd = InterstitialAd(this)
         interstitialAd.adUnitId = "ca-app-pub-3940256099942544/1033173712"
         interstitialAd.loadAd(adRequest)
         interstitialAd.setAdListener(object : AdListener() {
             override fun onAdLoaded() {
                 displayInterstitialAd(interstitialAd)
             }
         })

    }
     private fun displayInterstitialAd(interstitialAd: InterstitialAd) {
         if (interstitialAd.isLoaded) {
             interstitialAd.show()
          }
     }
 }