Connection to Digi One SP is not sending responses from modem.

Modem tech was used primarily before my time.

I’ve installed the realport driver on my workstation using com1 serial port.
I then set the Digi One SP to the port profile “real port”.
I connected a modem to the Digi.

When I connected to the Digi through com1 using putty, I get a blank terminal window with a black background. When I enter AT to test the connection to the modem, I receive no response.

I have changed the cable between the modem and the Digi to see if that was to blame. What can I do to troubleshoot that I may be missing?