Originally Posted by
NWIFlyer
This is what Timatic lays down as the requirements (my bolding):
Originally Posted by Timatic
Passengers must have:
- a negative COVID-19 NAAT or antigen test taken at most 48 hours before arrival. The test result must be in English, French, German, Spanish or accompanied by a certified Spanish translation; or
- a COVID-19 vaccination certificate showing that they were fully vaccinated with AstraZeneca (Vaxzevria), Janssen, Moderna or Pfizer-BioNTech, Serum Institute of India, Sinopharm or Sinovac at least 14 days before arrival; or
- a COVID-19 recovery certificate issued at least 11 days after the positive COVID-19 NAAT test result. The sample for the certificate must have been taken at most 180 days before arrival.[/QUOTE
There's absolutely no mention in there of what constitutes a valid certificate, so I can perfectly well understand the BA check-in agent denying you boarding until the necessary assurances had been received from the Spanish immigration authorities.
But if the OP was also already fulfilling the part in red, why deny boarding?