showBannerAd() {
  let bannerConfig: AdMobFreeBannerConfig = {
      isTesting: true, // Remove in production
      autoShow: true,
      bannerAtTop: false,
      id: "ca-app-pub-3940256099942544/6300978111"
  };
  this.admobFree.banner.config(bannerConfig);

  this.admobFree.banner.prepare().then(() => {
      // success
  }).catch(e => alert(e));
}