AdMob Free Interstitial ads need to be close after screen off

Ionic Framework ionic-v3
1

During review, we found that your app <>> violates our Monetization and Ads policy.

For example, By pressing the Android OS Home button to exit the app displays the home screen, but then an ad pops up outside of the app.

i have checked and this is correct
I have implement as per document , but i want to close the Interstitial ads if the user press home button,

can you pleases suggest

CODE-----------
let interstitialConfig: AdMobFreeInterstitialConfig = {
autoShow: true,
isTesting: true,
id: “ca-app-pub-xxxxxxxxxxxxxxxxxx”
};

this.admob.interstitial.config(interstitialConfig);
this.admob.interstitial.prepare().then(() => {
// success
});

///////////////////////////////////

2

You need to simply exit the app on back press in home page. use the following code inside platform ready event.

@ViewChild(Nav) nav: Nav; //Global Variable

platform.registerBackButtonAction(() => {
        if (this.nav.canGoBack()) {
          this.nav.pop();
        } else {
          platform.exitApp();
        }
      });