Groups wont be synchronized

I have created a group in Contacts app of macOS. And I have added some visit cards to this new group. But this group does not appear in the NC web interface. And the group won’t be synchronized with other gadgets which are connected with the respective NC account.

What am I doing wrong?

CardDAV itself supports two ways to store group information, one where the group name is stored in the CATEGORIES field of a VCard record (VCARD 3.0) and one where a group is created as a separate VCard (VCARD 4.0). Nextcloud only supported the first one!