I had that problem my oldest son was 3 and a few months when finally was potty trained and we rewarded him everytime he would go in the potty till he finally would go on his own. Try a chart and you cannot stickers on the days he goes potty in the toilet and you could try telling him when he fills up the chart with the stickers he can go to the store and buy a toy or chuck e cheeses or any reward you think of

Give him candy everytime he goes potty or clap your hands and show how proud you are of him for going potty.