Mag cards and RFIDs are nothing more than a storage medium for holding an (alpha)numeric code. This code can relate to a Member ID, which is a custom data field for an Entity (i.e. Customer), which in turn is tied to an Account.
There is nothing special about their use. Swiping a card emulates keyboard input to locate an Entity within SambaPOS. This simply saves having to type in a member ID using the keyboard.
An Account Type can be set to “Credit” mode so that when the balance reaches zero, it can no longer be used as a payment method. “Topping-up” or adding funds to an account can be done via Account Transactions and Account Transaction Documents and (optionally) with automation.
Your scenario is no different than any other Customer Account scenario.