You'll see more explanations when you look in the journey details.

To be able to say more, we would need to know which exact train it is (route, departure time).

Casi todos los trenes directos de Verona a Munich. 

The ECB (Eurocity Brenner) trains definitely carry a “toll” of 10 euro 2nd class and 15 euro first class.

If you get a reservation from OEBB.at it will include the toll.

A reservation only (3€) from oebb.at won't include this toll. If you indicate the "Interrail/Eurail” discount and then look for normal tickets, you'll find the 10€ toll, but a reservation will still be 3€ extra.

If you book a reservation via CD however, you'll find a reservation of approximately 10€ which includes the toll.

Many apologies, I was wrong - I got my reservation from Interrail reservations - First Class inc seat for 15 euro (+ 2 booking fee)

But it did include a seat reservation.

I confused it with a reservation via OEBB for Venice to Vienna.

@Carina Teatro Hello!
Please allow me to clarify that according to our timetable, (https://www.eurail.com/en/book-reservations) the ECB train from Verona to Munich has optional reservations. That means you can purchase them, however, you do not have to.  However, an additional supplement is necessary for this trip. You will need to pay for it before boarding or during the journey. This is an administrational/service fee.