Potty Training

My son is 2 years old. He knows when he is going poop as he goes and hides, and will tell us before he pees.

The issue is, he absolutely refuses to sit on the potty. Whether it is the big potty, or a toddler potty. He’ll sit on it fine if he doesn’t have to go, but if does have to go, it’s a whole screaming tantrum and absolute refusal to sit. I don’t understand this 😕 I thought he was afraid of the potty itself, but it doesn’t make sense if he sits on it when he doesn’t have to go. I’ve tried giving him entertainment, even candy. Nothing works!! We have yet to be able to offer him any sort of reward for going on the potty, as it hasn’t happened yet. If we catch him mid pee or poop, he’ll just stop and hold it until we take him off.

I am so frustrated. I know he’s ready. Any advice?