DAVx⁵ has been successfully tested with is a german web hosting portal.

DAVx⁵ settings

You will need different accounts for CalDAV and CardDAV.

Use "Login with URL/user name".

CalDAV Base URL:

CardDAV Base URL:

You have to grant external access for each address book: in the Web backend, click the context menu for an address book and grant external access to it.

You need a separate DAVx⁵ account for each address book and each calendar you want to sync with.