My son is 2years 2 months, and still have no interest in wanting to sit on the toilet. To be honest, he's scared of it!!

We've had the sit on potties (3 different types), ring on top of the toilet, lid under the normal toilet lid and he refuses to sit on it as if something is going to bite him. I don't know what to do, how are we meant to try and start if he doesn't even want to sit on it