Patent ID: 7870073

Claim:
A payment method, executed by a communication facility in a first location and a data carrier in a second location, different from the first location, for debiting a payment value unit from the data carrier, in order to pay for a subsequently performed service, the method comprising: debiting, from a memory value unit stored in the data carrier, a value of a debit value unit sufficient for payment for the subsequently performed service; setting a repayment limit, stored in the data carrier, to the value of the debited debit value unit; calculating a credit value unit, to be credited back to the memory value unit, by subtracting a payment value unit to be paid for an actually performed service from the debited debit value unit; making a determination, by the data carrier, that the credit value unit to be credited does not exceed the stored repayment limit; and crediting the credit value unit to the memory value unit stored in the at least one data carrier based upon a first key stored in the first location, but crediting only when the credit value unit to be credited does not exceed the stored repayment limit based upon a second key stored in the second location.