It can happen that Webtrees gives an error such the following
SQLSTATE[HY000]: General error: 1364 Field 'id' doesn't have a default value You can try to solve it, assigning an auto-increment default value to that field, in PhpMyAdmin
phpgedview: aggiungere matrimonio
Eccola la risposta in inglese: “If you open the individuals page then pick the “Close Relatives” you will find a link at the bottom of the page that will let you add a spouse to the person.
If the marriage is to a person that is already in the database there is also a link that will let you add then to that way.”