Montpellier - Barcelona will be a paper ticket. Barcelona - Valencia possibly, too.
The app seems incorrect: 34 EUR would be the price for Paris - Barcelona; Montpellier - Barcelona should be cheaper and 17 EUR (= 15 reservation + 2 booking fee) could be correct. 6.50 for Barcelona - Valencia is probably correct.
Be warned that the Spanish timetable in the Interrail website and app is incomplete; check the
RENFE website for all trains.
If you're in France, the best is to go to a ticket office. You then don’t pay Interrail’s booking fee or postage fee for sending a paper reservation (9 EUR).
ts half. For Fast trains IN ESpana you canNOT book online via this method. Thus this 17€ is the price for only TILL Barca. Best is to NOT use the online method as its too late. Go to SNCF counter in Mplr and let them do it. Maybe, if they are willing &able-which is by far not always the case with SNCF, they can even do the Spanish train, if not, you have to do it on that Sants estacion in Barca.
Also (I just flew back from ES today) amny, many trains do NOT run for now as so few pax due to covid. Best actual situacion inside ESpana. Brush up your spanish too!
Thank you very much for your answers! I’ll try to go directy to a ticket office to be sure then.