Yes, you must hold a valid ticket to travel on all MOB - GoldenPass trains (Regional, panoramic, mountain trains and funicular).
This means that all passengers are responsible for making sure that they have a ticket or travelcard. Customers must have a valid ticket or travelcard before the start of the journey (actual departure). The purchase and ordering process (tickets purchased digitally) and the acquisition of authorisation to travel (check-in) must be fully completed before actual departure.