I did 3 days ago just set the library to 3.1. Unless u need the newer library for some reason. When Appery.io update to a newer library I will post something
Dear Appery.io Community,
This is to let you know that we have just created a tutorial that could be useful for integrating AdMob in an Ionic 4 project. If this is still of interest to you, please check it here: https://docs.appery.io/docs/ionic-4-google-admob.