Send fax in UCP immediately fails with "initializing"

Dear FreePBX community,

My FreePBX setup concerns PBX Version 17.0.19.21, PBX Distro 12.7.8-2408-1.sng12, Asterisk Version 21.5.0.

I have purchased the commercial module Fax Configuration Professional to make use of the send fax functionality in UCP.

Previously, I used PBX Version 14 on Sangoma hardware (PBXact) which needed to be replaced. Therefore, I made a new install of PBX Version 16 on a VM and restored the PBX Version 14 Backup. Then I backed up this setup, moved to PBX Version 17 on a VM and restored the PBX Version 16 Backup.

I needed to update the restored configuration because of the not longer supported chan_sip. I adapted custom dialplans because of removal of macros and modified context names to correctly link to the hooks in Free PBX.

I got this configuration working and can process inbound and outbound calls. Also incoming fax are processed correctly.

The only thing that does not work is sending fax via UCP.

I have installed a Let’s Encrypt certificate, UCP does not report any errors. When I send a fax and watch the asterisk output via asterisk -rvvvv with default settings, nothing is output. Instead, the sent fax in UCP is immediately put into the failed bin stating “initializing”.

Does anybody have a hint as how to debug this problem?

Best regards,
Peter