From https://security.stackexchange.com/questions/186327/why-do-some-gdpr-emails-require-me-to-opt-out-and-some-to-opt-in :
As a consequence the "G29", the group of national data protection authorities in the EU, affirmed that if a user has no real choice, feels constrained, or will face negative consequences for refusing consent, then the consent given is not valid. The G29 therefore affirmed that GDPR guarantees that giving consent to processing personal data cannot be the counterpart of providing services.
Spanish law demands that anyone providing hospitality enter personal data into a database on every guest within 24 hours. Seems like we would have to start asking guests to sign a stupid consent form, and not let them stay if they don't. But that would violate what's quoted above. If we let them stay and don't enter their data, https://www.vacaciones-espana.es/rentalbuzz/policia-explica-el-proceso-de-identificacion-de-viajeros-en-vft says we are subject to huge penalties. If we enter their data without their consent, we AND the Guardia Civil are violating the law.
At least that's my untrained interpretation. What am I missing?