What gets prepended to the username when logging in usually "firmenname".
Can be left empty.
Change to your choice of domain name. E.g. DC=firmenname,DC=de . See also Distinguished Names | Microsoft Learn and LDAP ADsPath - Win32 apps | Microsoft Learn . Same in LDAP/AD group rights map.
You can enter a username/password combination and will see which rights it gets on the web interface.