Hi.
Sorry to here you don't get it work..
I see you are using USB-serial adapter for the nullmodem cable.
That could be the problem..
So if you have/can loan an old PC(XP os) with real serial comport, i would have tried that as it is working better for such jobs.
I will ask my brother for one of his old PCs with native serial COMport and send you feedback.
I awfully appreciate your care
All the best/Ciao
Lorenzo