NO! Could you show that part of the mail? Must be a misunderstanding or bad formulation.

These passes you mention are only for EU-young citizens and these are moreorless expected to know how trains work-though this can be quite different in other countries as where they live. Well over 90-95% of ALL trains that run in EUR are without any RES or with optional. But somehow about any newbee seems hell-bent on exactly using those trains that are the hardest to get and to RES-that always cost  extra -a few or a heap of €. This mostly concerns the hi-speed trains In FR/IT/ES!! and those in between and to there. This forum is brimming with that-and noone also seems to be a little bright in thinking her/his Q has been posted already a few million times.

dear anna B fra Sverige will also greet you and post a big overveiw of useful tips and links on howotodo RES all by yourself-often easier and cheaper too as via app/site. USE that!

There are different versions of the DiscoverEU pass. Exactly what does it say in the mail you got?

There is a pilot test, with some DiscoverEU winners that get reservations for free. Best way is to ask in the Discover EU Community.