How to handle prepaid product

A customer comes in every month and prepaids 100 coffees that he will consume as he comes.

Is there a way I can manage this with SambaPos?
I want to manage the units of prepaid product, not to have funds on his account and use that to checkout.

The reason is because I give a discount for this purchase so I want to track redeem coffees.


A custom field to track orderes as added would be simplest i can think of.