The pay isn't much anything substantial. Cambly pays 17 cents per minute, which comes to $10.20 an hour if you manage to teach the entire time. The difficulty lies in finding enough students to fill your time so that you make that number.
When you first begin and have no regular students and no rating to demonstrate your skills you won't be filling up all of your time and can expect closer to $6/h. Cambly directs students to you if you sign up for a "priority hour", so you'll always have students, but not always enough to fill your entire hour. I've been teaching on Cambly for several months now and have a good list of regular students, but I still only average around $8 assuming nothing goes wrong, like cancellations.
Because of this I would only recommend Cambly to someone, like myself, who lives in a part of the world where $6-10/h is enough to make a living.