Hello i Get this error from the ISP ( ISP has a cisco two)@Hostname
If the Cisco cube is essentially added as a SIP Trunk on the PBX you can just route faxs to a specific DID to 3CX's FAX server: https://www.3cx.com/docs/manual/fax-server/
Hello i think that the provider not enabling T38.The SIP response code 488 is usually due to CODEC mismatch. If your not sure if your provider does T.38 you can try enabling "Enable G.711 to T.38 Fallback [BETA]" as an option. But I got no experience doing this, just a suggestion.
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