Hi Victoria,

The aim of the mobile pass is to provide as seamless an experience as possible, so the ticket element can be shown from your phone at any time during the period of activation, as described in this handy guide:

If for any reason a technical malfunction were to cause this to fail, you would be able to get in touch with Interrail’s customer services and seek a refund for any penalty fares you’d been given by ticket inspectors.

The only printed documents you may need are a couple of very specific train reservations, but most of these are now also paperless.