What are the levels in kickboxing?

Depends entirely on the school.

Some kickboxing schools are based off Karate systems and retain the belts and grades.

Some kickboxing schools are based in MuayThai and hold a singlet system similar to the belts.

Some as Frank pointed out are just Beginner, Intermediate or Advanced.

There is no belt system of ranking in kickboxing like in many martial arts

Or you're good at it or you're not. Belts or ranks don't matter in the ring.

There is no ranking system. Real martial arts like kickboxing/muay thai make fighters, not belts.

Some kickboxing gyms got them some not... It depens. Like in my gym we got belts I think 6 or 7 and then the black belt Dan rankings.... But some gyms don't got belt systems. It realy depens on the gym.

There are three.

Beginner.

Intermediate.

Advanced.

Sometimes Intermediate and advanced are within the same class.

amateur

professional

same as boxing