I feel truly scammed here, not necessarily by Interrail, but by Renfe. Please state this clearly on the Interrail website for everyone to see before they buy an Interrail pass in order to travel in Spain.
You need a reservation with your name for most trains in Spain. However, most of the time you can only get it if you go personally to a big-city-station, where you might have to pay up to 40€ to get a paper ticket that you can only use in paper form. No web option, no phone option. Like in the XIX century. If you’re not near a big city in Spain, you basically have no chance (unless you know someone who is willing to go to the station for you and then send you the paper ticket via snail mail).
I can’t count the time, the money and the energy I have spent on this issue.