How to you enable monetization on YouTube?
In order to associate your Adsense account with YouTube channel, you need to first enable monetization on your videos, for this, your YouTube account must be in Good standing and fully complying with YouTube policies and community guidelines. You must have at least one video which is originally created and uploaded by You. For enabling monetization on your channel, please follow the steps and screenshot below.
Sign in to your YouTube account
Click on the top right where you can see your picture, and then click the setting gear icon as showing in the picture below: