A dispute resolution system for requesting a service provider to provide services so that the service provider can demonstrate to a service intermediary that a service consumer requested services. A service consumer that wants to start requesting services of the service provider registers with the service intermediary an end code of a sequence of code generated using a one-way function. The service intermediary provides the end code to the service provider. The service consumer can then using codes of the sequence requests the service provider to provide services. When the service provider receives a request, it verifies that the code of the request can be used to derive the end code. If the verification is successful, then the service provider can provide the verified code to the service intermediary as non-repudiatable evidence of the services requested by the service consumer.