That is strange, it seems that the user cannot be found. According to the debug message:
there is no user associated with this key. No key id set.
Did you complete the setup without any error?
Can you check on the server if the user is there and active by checking in the database:
select * from users where email@example.com';
select * from gpgkeys where user_id = (select id from users where firstname.lastname@example.org' order by created desc limit 1);
Replace ada with your username. Check if user is present, and set to “active” 1 and “deleted” 0. Check if gpg key exist for the user.
Then checks if the key is present in the keyring. There might be an issue preventing the key to be imported. Check if it is present in the keyring:
sudo -H -u www-data bash -c "gpg --list-keys --home=/var/lib/passbolt/.gnupg"
If it’s not try to see if you can import it manually:
sudo -H -u www-data bash -c "gpg --home=/var/lib/passbolt/.gnupg --import path/to/user/key.file"