Required software development freelancer for Cisco SIP dial-peer configuration job

We're looking for someone to configure dial peers by best practices. At this stage we have a problem that we cannot transfer calls. Inbound and outbound calls work. Call transfer between SfB users work. Additional task is to redirect FAX number to the external provider.

Caller: my mobile 0404xxxxxx
Calling to office number: 029302xxxx
Once call is answered I wish to transfer to some external landline number: 029194xxxx
Call transfer fails with SIP error:
AEDST: //3254/72A94F1D9C0D/SIP/Msg/ccsipDisplayMsg:
Received:
SIP/2.0 604 Does not exist anywhere
Via: SIP/2.0/UDP 172:5060;branch=z9hG4AAEE113D
From:

Skills & Expertise Required

software development