I guess that you are too early to make the reservation or what do you think? @rvdborgt @Angelo 

Ir is simply as for now not (yet?) possible to make a RES online for trains of CFR=the only company in RO that accepts passes. Plus that they have recently again got yet another system for bookings (in RO all normal tickets come as tied to a specific train/day etc.) and many staff seem-judging other reports-not yet trained on how to now serve the passholders.

But it is simply again totally completely unneeded to RES trains over barely 100 Km so long advance and with so much trouble. Just wait till there and visit counter on arrival for next trip

BTW-if this is the only trip you intend to do that day-forget pass, buy locally-and preferably even from a competitor with much better trains-there are several on this route

Brașov - Budapest is "a bit” more than 100 km, more like 700 km.

The train that leaves at 15:21 can be booked online via tickets.oebb.at and delivered via e-mail. Do NOT use "Seat only” but add the Interrail/Eurail discount and then look for normal tickets.

I suspect the other trains will release their reservations soon.

Note adding an interrail discount on oebb.at is done via the passenger choices, Select discounts and a drop box appears with some discounts. To find interrail/eurail option scroll to bottom and select see more. The interrail option is near the bottom of the new much longer list, just select and press confirm. It needs to be done for each passenger.