The server address has to be the IP not the hostname (at least in my environment)
| Setting | value |
|---|---|
| Server Address | 136.243.142.20:389 |
| Search Base | ou=rC3 2021 NOWHERE,dc=eventphone,dc=de |
| Search Filter | leave empty |
| Search Attributes | sn,telephoneNumber |
| Number Attributes | telephoneNumber |
| Display/Sort Attributes | cn,sn |
| LDAP over TLS | optional - use Port 636 if on |
This was tested with an Ascom IPBS2 as base and Ascom d62 DECT Phone