Potty training help

Dev

My son will be 4 in a few months. We’ve been potty training for 1.5 years. He goes pee fine in the potty but pooping is another story. I’m about to lose my mind.

I have him sit on the potty every night before bed and he always goes poop right away without a fight. But he’ll still have accidents the next day. He refuses to tell me he needs to go. I’ve told him a million times just tell someone he needs to poop or just go to the bathroom and sit on the potty.

He doesn’t fully poop his pants, he just leaves a little skid mark I guess because it slips out then he tries to hold it in. I make him finish on the potty every time this happens and he does that without a fight.

He knows better. How can I make him poop on the potty? I’m going to lose my mind.