Have multiple potties in multiple rooms (bathroom, bedroom, livingroom). Start with praising for every second he’s on the potty, even with clothes on. Make habit to set him on set times on potty (before bath, before bed, before you go out). Give the right example, you could take him to the toilet with you. There are some nice you tube vodeo’s which have toileting as theme, let him watch them while on potty.
Does he go to a daycare or playgroup ? Seeing other kids doing it might help as well.

I have the same problem with both my kids , never had a problem with my Daughter until last year. Now she wants someone to sit out front of door and wait she is now 9. But for my Son i was told it could be his Autism.

I sit my kids on the potty in front of the tv to start with.. Some kids prefer to be on the toilet from day one some dont.. My daughter started on the toilet and she hated the potty never used it.. But i have found the key is to keep them occupied while on the toilet or potty.. My oldest son started potty training sitting down and switched to standing up when he was tall enough.. My youngest is still learning to do a poo on the toilet and when i tell him to do a pee sometimes he does a poo instead and when he does we make a huge thing out of it and tell him how good he is… I have also learnt when your kid has wet themselves tell them its ok but also get them to sit on the potty as they sometimes have not finished going.. All kids will have accidents.. even when fully trained.. My son who is training is nearly 4 and still getting use to understanding his body but is getting there. I have also been known to let my kids used their leappad on the potty to keep them there long enough to do something and mainly so they can relax….

maybe it is too low or high for him, If ad could take him to hens toilet where there is a urinal,as unlike girls as we know stand up to wee,and aim eventually must be accurate. In summer I let my sons wee in garden, teaching them to hold penis and aim at spot trial and error but raised two sons I believe well. Normal function and praise is a good motivator