Backend system for a passenger transport system

A method for operating a passenger transport system with open ticket media and having a backend system, comprising:

• 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,
• receiving a change data set generated by an interface device in form of a validator device of the passenger transport system, the 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;
• wherein the second transport usage condition is a further transport usage condition different in scope of validity from or additional in scope of validity to the first transport usage condition, wherein in the second transport usage condition at least one of the following is defined:
• a plurality of transport trips for a plurality of full-paying users, at least one additional transport trip for a non-full-paying user, and a transport trip for a user with an additional luggage,
• wherein the change data set is included in a check-in data set and/or forms the check-in data set,
• changing 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 based on the received second transport usage condition,
• reconstructing a performed transport trip based at least on a check-in data set received from a validator device of the passenger transport system, the check-in data set containing at least the electronic medium identifier, and on a provided check-out data set containing at least the same electronic medium identifier, and
• generating a billing data set based at least on the reconstructed transport trip and a transport usage condition of the user data set linked with the electronic medium identifier.