I begun using Codementor, when I was looking for a little bit of side-income in my field. It is a very fulfilling way to do so, by teaching and mentoring other developers in how React works. I can totally recommend it.
I started using CodeMentor thinking it would be something similar to PeoplePerHour or Upwork, but this actually works! It's quick from signup to first project, weekly payouts, and a good platform for direct communication and mentoring. I think I got my first student within 24 hours after starting to use the site and my first payment in a couple of days later.
There's some minor technical annoyances, and you need to manually make sure your students accept you starting a session (or you're mentoring for free) but other than that, I mostly have good things to say about Codementor.
I like the idea how company can market themselves by giving a lot of value for community