I believe that this may be because MFA has not been set up.
XXX has been activated to the portal using the email address XXXXX so emails should be coming through.
To set up MFA for XXX, if you send her/him a new message on the message centre and ask XXX to check her inbox/Junk for emails from either xxx.accountantspace.co.uk or Wolters Kluwer and follow the steps to set up MFA this should sort the issue.
If you have any further issues please let us know.