I remember attending a talk by Dr Xavier Amador in which he described paying his brother $5 to take his meds.
There is a difference between rewards (positive reinforcement) and bribes.
You reinforce a behaviour but you bribe a person.
verb: persuade (someone) to act in one’s favor, typically illegally or dishonestly, by a gift of money or other inducement.
noun: the process of encouraging or establishing a belief or pattern of behavior, especially by encouragement or reward.
This is used with children with autism and this site explains it well in regards to children.