Using Banqer with Learning Contracts

I have integrated Banqer into my class contracts for a number of years. Students are "rewarded" for activities that they are already doing, and can choose from a range of additional tasks to earn more money. I find that lots of my students respond well to the motivation of finishing extra tasks for extra money.I have found that paying students for the things they already do (e.g. SSR, Teacher Groups, Basic Facts) is beneficial. Seeing their peers earn more money can be a great motivator for some students.It's also led to great class conversations of what is "fair"because some students don't like the fact that their classmates have a lot more money than they do - Should everyone get paid the same regardless of their effort? Is it okay to reward students who work harder? Is it fair that people who are sick or go on holiday miss out on earning opportunities? What is worth more - quality of work or quantity?