Once you have purchased your pass and before you travel, it is essential that you book and get your ticket for the day and the train you are interested in, what is known in railway jargon as "validation". You can do this at the ticket offices at stations, self-service machines, on the phone (912 320 320), travel agencies or through the Renfe app.
All Avant (mid-distance high-speed) passes can be cancelled at no cost, as long as you have not made any arrangements with it. If you have already made an arrangement, but have not yet travelled, you can cancel it with expenses (15% of its price).