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