Potty Training

My son is three and a half and we have been struggling with potty training. He knows what the potty is but we can only get him to pee in it if we ask him to go, he doesn’t go to the bathroom on his own or tell us he needs to go. He has yet to poop in the potty at all. I feel like he’s behind the curve for potty training for his age and he’s starting to outgrow pull ups. We’ve tried incentivizing going to the bathroom but that hasn’t really gotten us anywhere either. Any advice would be appreciated.