The Spanish entry travel requirements have been updated and from the 1st February you must have had your final dose of the vaccine within 270 days of arriving into Spain.
If you’ve received this more than 270 days prior to travel to Spain, you must be able to show proof of a booster jab (which must have been taken at least 14 days prior to travel).
Full details can be found on this link: https://www.gov.uk/foreign-travel-advice/spain/entry-requirements