On 6 April the resolution @sanidadgob was published in the BOE modifying the sanitary controls to be carried out at the points of entry to Spain. Only passengers who do not have a EU Digital COVID Certificate must have a SpTh QR code. More information here

In order to enter Spain, all passengers, regardless of the country of origin (except children under the age of 12 and passengers in international transit), must show one of these documents:

• An EU DIGITAL COVID CERTIFICATE OR EU EQUIVALENT of COVID-19 vaccination or a negative certificate of an active infection diagnostic test or a recovery certificate after having this disease.
• SpTH QR. If you do not have the EU Digital COVID Certificate or equivalent, you must complete the SpTH Health Control Form, manually entering the details of your vaccination, recovery or diagnostic test certificate.

In the case of a complete vaccination schedule, you should check the validity periods: this certificate will be valid from 14 days after the administration of the last dose of the complete vaccination schedule and will be valid up to 270 days from the administration of this last dose. The vaccination certificate with complete schedule for children under 18 has no expiry date. Thereafter, in order to be valid (people aged 18 and over), the vaccination certificate must reflect the administration of a booster dose. These certificates will be considered valid from the day the booster dose is administered. More information here