Patent ID: 8595131

Claim:
A method for acquiring a service offered by a service provider over a data network on presentation of a cash card having data stored thereon, said data corresponding to money in electronic form, by carrying out first a prenegotiation phase to order the service and subsequently a transaction phase including a compensation phase to make a contribution for delivery of the service, the service being ordered by means of a user end system that includes the cash card, from the service provider, the service provider thereupon calls a clearing center which subsequently enters into a data exchange with the user end system, to call for there from a necessary contribution in the form of certain data required for acquisition of the service, the method comprising steps in the prenegotiation phase of: at the user end system, determining an individual identifier of the cash card, for use in the transaction phase that includes the data exchange that calls for the contribution in order to homogenously link the ordering process with the following compensation process; at the user end system, sending a first prenegotiation message including the identifier to the clearing center; and at the user end system, receiving the identifier back there from the clearing center with a second prenegotiation message for acknowledgement; wherein the compensation phase further comprises using the identifier to effect a data exchange in which the money in electronic form stored on the cash card is reduced by the amount to be paid and a corresponding amount is credited to the clearing center.