I have tried every recommend trouble shouting remedy described on the support site.
If the question is not obvious by reading the symptoms, it is, "How do I send a fax from my computer?"
Symptoms:
From printer, send fax to fax test number. Result: fax was sent back acknowledging success.
uninstall drivers and software.
reboot computer,
install software,
reboot the computer
open HP Envy 7640 software by double clicking on icon
click on [fax] tab
Click on [Send a fax] ... eventually "Send Fax - HP ENVY 7640 series (Netowrk)" dialog box appears.
click on [To ...]
drop down dialog box with [Fax Contacts and select [Fax Phonebook]
check box [ ] 1 FAXBACK SERVICE 18884732963
Click on [Done]
click on the (+) of the Add Cover Page icon (clicking any where else is fruitless)
Enter "test" in Subject field
click on [Done] (now the [Add Cover Page] Icon looks like a cover page icon with an (X) in the upper right corner)
Click on [Send Fax]
A gas gauge bar appears briefly
wait ...
(no dialing sounds from printer, all is quiet)
wait longer ...
(no dialing sounds from printer, all is quiet)
wait longer still ...
(get frustrated with yet more substandard HP software)
Oh yeah, another frustration: opening the the HP ENVY 7640 series (Network) Toolbox [Device Information] tab
yields a box entitled "Serial Number" When trying to contact support (but you can't actually contact support) the serial number is requested. This serial number is not accepted. one must remove (in my case) the last four characters.
Model Name: ENVY 7640 e-All-in-One Printer series
Firmware Version: NSM5CN1830AR
Service id: 27093
IK Number: 56-20200304-0
(unlabled box) V1: 57,56
Software Version:040.013.1176.1978
Printer Driver Version: 20.80.02.7578
Installion IO: Ethernet (Multicast)
(the network works just fine, how do you think I got all of these other numbers?)