Is “message us when you arrive” a clear enough late check-in arrangement?

Lidia reads the accommodation message aloud. “Just message us when you arrive.”

Gavin closes the booking app. “There. Sorted.”

Their flight into Seville is scheduled after the property's stated reception closing time. The listing says late arrivals require prior arrangement. Lidia has sent their expected arrival details, but the reply does not explain whether someone will wait, where they will collect a key, or what to do if their arrival is later than planned.

Gavin thinks another message would be pestering a host who has already agreed. Lidia is comfortable with self check-in if that is the arrangement; she wants the actual instructions before they are outside with their bags. They are still at home and can clarify it now.

What would count as a clear answer before departure? In their illustrative comparison, a different first-night property with overnight reception would add €45. They would rather keep this booking if they can understand how they will get into it.