Abstract: A backend system for a passenger transport system includes: data memory for storing at least one user data set containing at least one electronic medium identifier authorizing the execution of a transport trip and at least one first transport usage condition linked to the electronic medium identifier; a receiving module configured to receive a change data set containing at least one second transport usage condition, at least one first time date and at least one user identifier for identifying a stored user data set; a change module configured to change the linkage between the electronic medium identifier stored in the identified user data set and the first transport usage condition for at least one future transport trip; a trip reconstruction module configured to reconstruct an executed transport trip at least based on a received user identifier; and a generation module configured to generate a billing data set.