Just show the page of the activated pass. Go to “My Pass”, click on your active pass of that moment and show that if they ask. You don’t need to show the ticket/qr-code.

It’s the page with your name, booking reference, validity period, used travel days,...

To receive the discount you need to show that you have a valid pass in the app when you buy the tickets. You don't need to use a travel day if you only get a discount. 

Thanks for the information!

Also note that in this region off-season there are frequently other special offers that may work out even cheaper as half fare of sky-high normal. Often they include complete round tours (like to Rigi up and down via 2 different rails)

Thanks for the tip! I will double check if there are other better offers when I buy the ticket.