A third party sip-phone was getting back 403 Forbidden after sending an Invite to Conference Factory URI as host to initiate ad-hoc conference with cucm 12.0. But SIP trunk messaging guide says "The conference initiator calls the conference server us...

I have been trying to set up an ad-hoc conference with a third party sip-phone as a host. But I am getting 403 Forbidden with "unknown calling DN" after I send an Invite to conference factory URI to initiate the conference. From SIP trunk messaging g...