If you're interested, we have a Proxmox backup of an Incredible PBX 2021-D platform with Incredible Fax already enabled. You simply need to put the image in /var/lib/vz/dump and put the Debian 10.13 ISO in /var/lib/vz/template/iso.

Then you can run qmrestore vzdump-qemu-ipbx2021dfax.vma.gz 777 to create a 777 VM. For Incredible Fax, go to /root and run avantfax-email-change to set the email address for delivery of faxes. Then run avantfax-pw-change to set the admin password for access to the AvantFax GUI. Run admin-pw-change to set the FreePBX admin password. Done.

For use on same server or multiple VMs: rm /var/lib/dhcp/dhclient* && reboot

If you need either the vzdump file (4.5MB) or the Debian 10.13 ISO (3.5MB), just send me a DM and I'll provide links to download with wget from your Proxmox server.