DP750 Can't conference between handsets

#1

I have both my handsets set to different pbx extensions, when I try to conference with the other handset I get error 512. Both are working in and out but only do I receive and issue when I try to have one handset dial the others extension and or do a conference.

#2

Nor can I transfer a call.

#3

What’s your accounts HS mode?
image

What’s the line settings? are they assigned to the HS correctly?