Indeed, our api definition that you can find that way or at https://open-api.netlify.com does not include all possible and existing calls, including that one.
What Luke was trying to describe is that you would use the UI to do the operation one time, and watch in the browser dev tools, and take the call we made and you can reproduce it on other sites to programatically enable.
This article has a more thorough description of how to do this: [Support Guide] Understanding and using Netlify's API