Royal Decree 933/2021 regulating the obligations of documentary registration of guests:

Being, like many other establishments, dissatisfied with the regulations, we are forced to follow the decree established by which the number of mandatory data to be collected is increased.

In addition to those already established:

1) First name.
2) First surname.
3) Second surname.
4) Sex.
5) Identity card number.
6) Document support number.
7) Type of document (ID card, passport, TIE).
8) Nationality.
9) Date of birth.

The following data are extended as mandatory:

10) Complete address (usual place of residence)
11) City (usual place of residence)
12) Country (usual place of residence) 13) Telephone 14) E-mail 15) Relationship between the travelers (in case any of them is a minor). (Usual place of residence)
13) Telephone
14) E-mail.
15) Relationship between travelers (in case any of them is a minor).

The obligations contained in this new passenger registration regulation apply to the entire Spanish territory; however, there are exceptions in two autonomous communities: Catalonia and the Basque Country.
Official link:
Real decreto