I am really surprised a child so young is capable of all this, probably too young for a sticker chart or lolly reward. Positive reinforcement and congratulating him when he goes

Try to make it fun for him, give him some books or something he likes to play to when he is using the potty.

18 months is a bit too soon to ask this of a child. You keep a track of time and tell him it’s time to go to potty. You can make a routine of every couple of hours. Make certain that he know what he is to do after potty. Washing hands and flushing the toilet after every entry.
Good luck with this..

My son was fully toilet trained day and night by the time he was 2 but I still had to constantly remind him to tell me when he needed to go for a long time after. They get so distracted with what they are doing that they don’t even think about it. Your little one is still a bit small remember and take himself yet but it won’t be long. Just keeping telling him to tell you when he needs to go and encourage him to hop on himself and he will soon get the hang of it!