Hi chazzwick,
First of all, before publishing a game on a store, make sure everything works as expected. It is very rare that something that is not working when you test your game will suddenly work when the game is published. Unfortunately you will need to update your game on the Play Store.
If you want to use AdMob, you have to chose between the built-in support and this extension. It is not a good idea to use them at the same time. If you only need to use normal banners and show/hide them at the bottom/top of the screen, you can simply use the built-in support. If you want to have more control over your ads, you should use the AdMob extension. So chose what fits you the best, but chose ONLY one. I have never tried to use both of them at the same time, but it may cause some issues.
Under Settings > Mobile > Monetization, you have to use your Ad Unit ID, not your publisher ID even if it says so. In a previous version of AdMob, it was required to use your publisher ID, but it is no longer the case. You MUST use the Ad Unit ID. I will ask to Jon to change "AdMob Publisher Key" with "AdMob Ad Unit ID" to avoid confusion.
Make sure you don't have any whitespace before and after your actual Ad Unit ID.
Let me know if you solve your issues!