Is there ringing voltage present at the all in one's jack?
Is the ringing signal 90V/20Hz?
Is the machine provisioned to receive faxes?

I "FEATURE 00"

As their vendor you have provided no info to the layout or what you have done so far to fix it.

Did you call the manufacturer?
Did you send a tech to site?
Are they all the same model?
Are the jacks looped to the demarc or is the phone plugged into the back of the machine?

"Fax (Party!)."
What does that mean?

"Is the machine provisioned to receive faxes?"
Agree, Since you say this issue is at multiple sites I would also wonder if the fax is not programmed to answer, or they have a flaw if they are all the same make....which we don't appear to know.

As you see we have rather questions than suggestions so I suggest you first gather then share the info when posting.

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www.curlycord.com
Toronto, Canada

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Thanks for the insights:

Did you call the manufacturer? Attempted, has been a real challenge so far but will be trying more when we roll on these more aggressively
Did you send a tech to site? Yes, we have been to the sites to do a survey of issues and equipment and connectivity layout
Are they all the same model? No, various models, a few HP and a couple Brother
Are the jacks looped to the demarc or is the phone plugged into the back of the machine? It appears looped to demarc, phone(s) is sharing the same landline as the Fax, etc...they have to warn their employees not to use the phone prior to sending a Fax - same line but plugged into different jacks I noticed on each machine the cord was plugged into the 'phone' port on the Fax machines and not the 'Line' port as well.

"Fax (Party!)." Setup like a party-line, phones and Faxes are sharing

Additionally, the company is working to bring in a separate landline for the Fax machines at each site in the near future. But a good quick fix on some of thee would be a good start.

first fix is to move the cord to the line port not the phone port, the fax will never answer that way.
Mike

Thanks, much better clues.

"Fax (Party!)." Setup like a party-line, phones and Faxes are sharing

I think you need to expand on this as to how it works.
I thought party lines were absolute.
You would call one specific number and it would ring a certain pattern therefore the multiple sites would know if to answer or not.

There is Ident-A-Call of sorts but that's for a single site only.
You have two phone numbers going over the same pair of wires.
You install a ring detector that has two outputs/jacks, it detects the ring pattern and sends it to the correct output.
So if you have this service from the carrier but not the detector installed then this could be the issue.

Either of the above two might be your issues.

Most fax machines these days have voice detection which knows weather to answer the fax or to send the voice call to the voice port on the back, in this case:
You should have just one POTS line going to the fax and the phone pugged into that back of the fax.
Or you could also purchase a line share device to accomplish this.

"the cord was plugged into the 'phone' port on the Fax machines and not the 'Line' port as well."
Assuming you mean the line cord from the wall jack and not the phones cord, then this would probably be your issue.

I would expect Mrs Whiggins to plug the line cord into the phone port but not a tech.

Suggest to send a seasoned tech to a site to have a better look.

Consider Faxing to the cloud option too.

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www.curlycord.com
Toronto, Canada

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Depending on the cost of the second line you may consider a Viking fax spliter. It is a one time cost device not a monthly recurring fee.

https://www.vikingtelecomsolutions.com/phone-equip...

Dermis and feline can be divorced by manifold methods.*
*(Disclaimer for all advise given)--'Version Dependent'

Thanks all for your insights and suggestions!