Anyway, it seems cordova-plugin-admob-free isn’t compatible with iOS because it still uses UIWebView… I had to remove it from my project.
I will try to find another way to have it working on both platforms.

Nice explanations! I finnaly had it working but is there a way to permanently set the meta-data in AndroidManifest.xml, build-gradle and AdMob.java, which are overwritten everytime quasar devis called?