Hello, I'm a voip specialist with over 10 years of experience working on the TS department of a Voip company; I can install, troubleshoot and customize many SIP devices including: softphones, ATAs, IP-phones and PBX systems. I read your project description, and if you can share what error you're seeing I may be able to help, I don't see any attachments, maybe you forgot to upload the screenshot ? Anyway, I can run a couple of tests on your FPBX server and pin-point what the problem is, I'm wondering though if you're using the fax-pro web-form to send the fax or a regular fax-machine. I'm available through chat to talk more.
Thank you.