The extension discussed in this thread is ancient and has never really been used in production. It was one of the first extensions ever created to test the feature. @sergey.lerg created a proper AdMob extension a long time ago. At first it was rev-share and recently change to paid access. The old rev-share version is still available:
Another alternative is to use Enhance to inject AdMob into your APK: https://defold.com/assets/enhance/
Or switch to UnityAds: Def Video Ads
A final option would be to fix up the extension discussed in this thread, but that’s probably the most difficult if you haven’t worked with extensions before.