They are just not accepted by the conductor. But those policies can also change in the (IMO) "right" direction, e.g. the German Deutsche Bahn changed their poli

They are just not accepted by the conductor. But those policies can also change in the (IMO) "right" direction, e.g. the German Deutsche Bahn changed their policies a few years ago and now digital tickets are accepted[1] in PDF form on digital devices, while they previously were not. [1] https://community.bahn.de/faqs/muss-ich-mein-online-gekauftes-ticket-ausdrucken https://community.bahn.de/faqs/muss-ich-mein-online-gekaufte... (german source, just saying that it can be used in the app or in PDF form on your smartphone, tablet or notebook)