Go to Developers Console and click Enable APIs and services:

Enable AdSense Management API:

Go to OAuth consent screen in the left menu and create consent screen settings, fill in Authorized domains field with

Next, go to Credentials section in the left menu and create new OAuth credentials. Select Web application and copy JavaScript origin URI from devtodev settings -

Save credentials and copy Client ID and Client Secret:

Go to AdMob settings and copy Publisher ID:

Fill you app bundle and copied fields into devtodev and enable integration: