Group Office is an enterprise CRM and groupware tool.
Enable synchronization
Before trying to set-up sync: Enable CalDAV/CardDAV for your clients in Settings → Synchronization (see Group Office wiki).
DAVx⁵ settings
For CalDAV use: /caldav
(e.g. https://server.example/caldav
)
For CardDAV use: /carddav
(e.g. https://server.example/carddav
)
Contact group method: No CardDAV contact group support. Choose "per-contact categories" as contact group method to minimize problems.
To use both CalDAV and CardDAV with a single DAVx⁵ account, configure well-known URLs (recommended).