T48 make calls to self

[bsanders]

Good Day,

I have two Yealink phones (T48 deskphone and T46 conference table) in a large office with the same extension. I need to be able to dial my own extension to call between phones. I can do this with the T46 but cannot with T48 (disconnects immediately). Any ideas?

Using:
3CX v12 sp6.1
T46 (28.71.0.224)
T48 (35.72.0.225)

thanks.