Go to "Apps" and Add App, you will be asked if you have published the app on Google Play or on Apple Store, for now press "NO", but after that you published it you have to come back and link your published app to the app you created now in Admob.
Enter the App name and the platform and press "ADD"
Once done you can create a Banner ad and an Interstitial ad and place its ids in the constant file, you will also be provided with the Admob App Id replace it also in constants
You also have to change the app id in "android/app/src/main/AndroidManifest.xml" in <meta-data android:name="com.google.android.gms.ads.APPLICATION_ID" android:value="ca-app-pub-1469570455778464~1228577141" />
For Admob on ios, you have to change your Admob App Id in GADApplicationIdentifier located in ios/Runner/Info.plist"
Go to lib/config/AdmobConfig.dart and let's start configuring Admob.
Replace the Banners Ad Unit Id and the Interstitual Ad Unit Id with your ids.
