Old school serial modem not found by VSI-Fax

I have a MultiTech modem on a serial port that I can dial using command line, but VSI-Fax cannot see. How do I have the system know it's there? All I can find is info on USB modems.

Everything I've seen in these portals show how to connect a USB modem, not serial. They also discusss going to System/Add Hardware, which I could in RHEL 5, but no longer exists in 7.

Anyone have an idea, aside from not using a modem. I'm stuck with it due to a program the company uses that requires it.

Thanks in advance.

Cec