Carlos asked us to share a full copy of our ID's over Whatsapp, saying that it's the law. We sent a copy with watermarks but he claimed this was not allowed. This is not in-line with EU regulation and we did not think sending a full copy of our ID over Whatsapp was a good idea because of the risk of fraud.
The Schengen convention and Portugese law require hotels (and by extension Airbnb hosts) to gather information about their guests, such as name, nationality and document number of a valid ID and submit this via an online system. It does not however require a full copy without watermarks, and EU data protection laws (GDPR) forbids it as there is no legal requirement.
Unfortunately Carlos was not very accommodating to our concerns and pressured us into sending a copy by threat of having to leave the accomodation. We offered to show our IDs in person, which he could take some info from if needed - but he did not want to accommodate. We were not informed of this requirement beforehand as it's not anywhere in the listing.
This left a bad taste for us, which is unfortunate because the apartment truly is beautiful and Carlos was otherwise nice.