Regional trains in Italy*
Yes, the DB-ÖBB Eurocity needs a 10€ fee for the italian part, wich can also be bought online via ÖBB. Interrail App often says that you need a reservation wich is not true, you need the fee. Reservation is optional. At Ticket offices of Trenitalia and DB you get with the fee a reservation for free.
Important: The railplanner app is not retailable, because often informations are wrong or train miss.
Even if you ´forget´ this the conducor will find you and then ask for payment-it has been noted they now start/or maybe have already-to ask for higher price in train as beforehand.
Alas, it is NOT possible to forego this, as a leg in South-Tirol/ITaly area has ow its own regional trains, not taking pass-so you would also have to pay for that sector till Brennero. But its a little less as 10€