Hello,

Do you still remember the time of your own childhood? What was it like when adults promised you something and in return you met their expectations, but they didn't meet yours? Children are memory experts and don't forget who kept their word.
If it is your own parents who teach the child the first disappointments, this is the normal course of events because no mother and father is perfect, but from now on it might be difficult for you to keep your son motivated to be a good learner through rewards. You may no longer have an easy time getting him to believe what you promise him.
I wish you every success in regaining his trust.

Greetings.