When the child is ready, training can happen almost by itself, just as learning to walk and talk are natural developments once a child is ready. You don't have to reward a baby to start walking, and when the child is physically and emotionally ready; rewards usually aren't needed for potty success, either. Though you can and should celebrate, just as with walking!
You can start the process earlier, but the child will seldom be truly trained until they are ready – usually it's the parent who get trained, to take the initiative to get the child to the potty. For boys, training is often pointless before the age of 3.5 or sometimes 4 or so. Pushing a child will often make him resistant, and everything will take longer.
My suggestion is that you back off for awhile on requiring him to use the potty, put him back in diapers, and let him know you are confident that he'll do this big-boy step when he's ready. You can continue with positive messages, books and videos about using the potty and how the body works, puppets going potty, etc. Point out occasionally that any "big boy" your son shows admiration for uses the potty (don't overdo this, or your little guy will get rightfully sick of hearing it and tune you out).
And then trust the process. That's the hardest part, probably. But enter "potty training" in the box at the top of the page to read many stories by moms who did exactly this, and their kids were suddenly ready to take the initiative themselves.