Abstract: A method for controlling exposure to liabililty for non-payment by a service consumer and controlling costs associated with requesting payment when a service provider provides services to a service consumer, the method comprising: specifying a number of services within a billing unit for the service provider and the service consumer; generating a sequence of codes from a start code to an end code, the number of codes in the sequence corresponding to the specified number of services within the billing unit; providing the end code to the service provider via a service intermediary; when the service consumer request a service of the service provider, providing to the service provider one of the codes of the sequence from which the end code can be derived; and when the service provider has been provided by the service consumer with the start code, requesting payment for the billing unit.