Mobile ad mediation implementation?

From what I've seen online, using ad mediation in your apps is the right thing to do to increase ad revenue (when different ad networks bid against each other).

I tried to implement MoPub mediation (with Admob added as an adapter), but I don't have experience setting this up. I've read through the mopub mediation docs, but it's not working. I posted some super beginner questions that should seem obvious for people who have implemented mediation in their apps.

Are there any good blogs, youtube videos, etc. explaining how to implement iOS ad mediation? I think it's common for new app developers to add AdMob and not worry about mediation (myself included).

P.S. Ads are one option for indie app developers to monetize their apps. While IAP or subscriptions are great, they don't work for all apps.