Using the example in the previous version of this document, calling prepareInterstitial(adId) resulted in an
"-[__NSCFString count]: unrecognized selector sent to instance"
exception. This was alleviated by changing the call to prepareInterstitial({adId: adId})
(e.g. passing in an options object vs. just the adid string)
remove the dash "import { AdMob, AdMobOptions, AdSize, AdExtras } from '@ionic-native/ad-mob';" to import { AdMob, AdMobOptions, AdSize, AdExtras } from '@ionic-native/admob' because typescript will not import the specified clases