FAX Support - Why are inbound faxes being mistaken for voice calls?

Outbound faxing is ok, but inbound faxes fail to a fax machine on ext yyy.  There are error messages in the error logs:

Incoming call for extension () from number (xxxxxxxxxx) failed to be received as a fax because it was a voice call.
Fax Failed Received an incoming fax from (xxxxxxxxxx) but extension (yyy) is not a valid extension to accept faxes

• Check Setup > Call Routing > Incoming Calls

• Check that the Incoming call rule is set to 

  • Route all Voice Calls and Faxes on number zzzzzzzzzz from Any Provider to extension yyy.