SOGo is fully supported and trusted open-source groupware server with a focus on scalability and open standards.
CalDAV/CardDAV path: /dav (e.g. https://server.example/SOGo/dav)
If well-known URLs are configured, you can use the host name only (recommended).
There's a server problem regarding REPORT addressbook-query requests, which has been fixed with SOGo 2.3.3. Make sure you're running SOGo 2.3.3 or newer, otherwise contacts synchronization will not work.