potty training

my son will be 3 in december & is still in diapers 😭 we live in a newly built apartment with carpet so we can’t let him run around without a diaper or pull up. we ask if he wants to go sit on the potty and tell him if he feels the need to go, to tell us and we’ll take him. he’s gone potty on the toilet before and he knows to flush it but he won’t tell us when he needs to go. when he does go on the toilet, we reward him with m&ms, or a small piece of candy but now he expects candy for even sitting on the toilet 🫠 we also try to keep it light w the treats because he’s highly affected by sugar. any tips??? we also have a newborn and diapers for 2 kids isn’t cheap :/