For those using the Mobile Master Ads. (This is a free upgrade in the Construct Master Collection.)
Try the Mobile IronSource Collection instead, here's the tutorial and documentation.
It has complete ad-network mediation, and complete SDK features. I have made sure it's top quality, it's a premium client order, so you can rest assure there won't be any issues with Construct 3.
IronSource is a top tier network and you can integrate all the ad-network mediation you use, including Google Admob. I have written the native libraries myself with dedicated support for Construct 3 and the C3 Build Service, it also auto updates the libraries on every build.
I will be writing the Mobile Admob Collection soon, just to replace the Mobile Master Ads (free update). But, IronSource is a better network, and I have supported complete ad network mediation with it.