A small number of countries — the UK, Ireland, Finland, Malta and Norway — require dogs to be treated for the tapeworm Echinococcus multilocularis shortly before entry, because they're working to keep the parasite out of their territory entirely. Spain is not one of them, and MAPA's own guidance page states this plainly: there's no tapeworm treatment requirement for a dog, cat or ferret entering Spain.
This matters most if your trip continues past Spain into one of the five countries that do require it. MAPA's guidance is specific that the treatment becomes relevant only when leaving Spain for Ireland, Malta, Finland, Northern Ireland or Norway — and only for dogs, not cats or ferrets — timed to the window those countries set, typically 24 to 120 hours before arrival there.
If your route is the reverse — leaving one of those five countries and arriving in Spain — the treatment you had done for that country's entry rules simply isn't needed again on the Spanish side. It's one of the more straightforward parts of the paperwork, once you know which direction the rule actually applies to.