Adding DAV to Kmail fails

Hi,
I try to add my NextCloud CardDAV addressbook:

  • Add DAV-groupware-source
  • Fill in credentials
  • Select Nextcloud as server
  • Fill in host and path
  • Test connection
  • Result: an error occured: invalid answers from backend

Is that a nextcloud backend or Akonadi? In the logs from NextCloud I don’t see anything related.

How can I solve this? When I select “Finish” I get the opportunity to edit the info, but, no account is added.

EDIT: if I specify the path to my addressbook more precisly and select “fetch” I get the same error (invalid answers from backend).

EDIT2:
Altough in Kmail I don’t see the Nextcloud account, in the Akonadi-console I see 3 times Nextcloud and 2 times DAV-groupware. I could try delete those, but when opening Akonadi console I get a warning not to edit anything unless I know what I’m doing, and I don’t :-).