I was following along FAX CNG detected but no fax extension but wasn’t too sure if I needed to put anything in the Advanced -> Asterisk Sip Settings -> Chan SIP settings configuration. I added the
exten => fax,1,Noop(Fax detected!)
same => n,Dial(Local/[email protected])
In the extensions_custom.conf file and reloaded Asterisk and fax detection is turned on for my DID. I was doing this because we have one client that sends us a fax but the PBX is always saying Fax CNG detected, but no fax extension.