Potty training

How do you get your toddler to sit in the potty?? My toddler is 2.5 and he’s been holding his pee in as long as he can and says ow ow right before he pees. I took him to the doctor because I thought he might have a uti but it came back negative. I feel like he’s doing that because he’s ready to be potty trained but he refuses to sit on the potty no matter how positive we make it it walkways ends in tears. I got a little boy doll that pees that came with a little potty and he loves the toy and tells it where to pee on his little potty and will clap for it when it pees but will still not sit on it. I know once he lees for the first time it will click but idk what to do to make him sit on it. Any advice will be appreciated! I’m at loss on what to do