MasterCard will require merchants to perform partial authorizations and real-time authorization reversals for debit and prepaid card transactions, in addition, merchants will be required to support available balance responses for prepaid card transactions.
This shouldn't have anything to do with ZenCart. This is for swiped transactions using a pin-pad I'd bet. I'll check with my contact at Radiant Payment Systems tomorrow about this and get a definitive answer from the merchant service people for Counterpoint.