I have a PBX UCM6302 Grandstream, and inside I have Snom320 phone. I'd like to have in the function keys BLF of the other extensions. This works fine with Grandstream phones but also Yealink, Gigaset, Alcatel etc, but with this Snom320 I have the lights off. What do I have to set to it? Is there an incompatibility? (FW Snom 8.7.3.25)