The terminals are capable of processing pre-paid cards. They support various payment methods including Visa, Mastercard, Discover, and American Express, which are common issuers of pre-paid cards. In general, pre-paid cards can't be overcharged, it will just decline and not take what's left. So the amount charged has to be equal to less than the current balance of the card. In some cases, the card also has to be activated before use, depending on the provider.