A discounted season ticket, known as "residential" travel. You need to submit form number XX01
here and get approval from RSTL. In the form, you can choose whether you want to buy the season ticket via RST Online or at a ticket office.
If you choose to buy it via RST Online, you can renew your season ticket online without having to fill in form XX01 again. If you choose to buy it at a ticket office, you'll have to fill in form XX01 and wait for the approval to come through, each time you renew your season ticket.