ionic 3 - AdMob is experiencing an error while placing it in APP

When I put AdMob in my ionic application it looks like the picture below:

What would be the mistake to not be showing ads?

Code I use:

displayBanner() {
if (this.platform.is('cordova')) {
const bannerConfig: AdMobFreeBannerConfig = {
  // we will just use a test id for this tutorial
  id: 'ca-app-pub-9249962217154699/5959043893',
  isTesting: true,
  autoShow: true,
  bannerAtTop:true // default is false
};

 this.adMob.banner.config(bannerConfig);

  this.adMob.banner.prepare().then((result)=>{
    console.log(result);
  },(reason)=>{
    console.log(reason);
  });

}

 }