We would like to know more. Go here: https://www.youtube.com/features > Click on monetization and share the screenshot of the page that you see. This would help us look into the issue better.
Thanks for the screenshot. Monetization can be disabled for various reasons. Depending on the issue with your channel, you may be able to take steps to reinstate it. Our Help Center article provides more info on this: https://yt.be/help/Uv9P . Hope this helps.