Serial Button Binding not working never triggers event

I am using the new Serial Button Binding:

I have a thing setup:

serialbutton:button:myButton "myButton" [ port="COM4" ]

I see the thing initialising in the event log:

- 'serialbutton:button:myButton' changed from UNINITIALIZED to INITIALIZING
- 'serialbutton:button:myButton' changed from INITIALIZING to ONLINE

I have a USB to Serial adaptor plugged in, I am running Windows 10 and in Device Manager I see the adaptor has been assigned COM4

I have an RS232 min tester plugged into the adaptor and flying leads from the other end.
My mini tester shows the following:
RD - off (zero voltage)
TD - red (negative voltage)
RTS - red (negative voltage)
DTR - green (positive voltage)
all others off

If I short pin 2 and 7 (RD and RTS) then it pulls RD to negative (red) but no event is triggered in events.log.
I have tried with another USB to serial adaptor and I have the same problem.
If I connect my mini tester to an adaptor on a COM port that has no SerialButton thing assigned to it then the DTR ‘Data Terminal Ready’ LED is red so I assume that the binding is correctly listening on COM4 it just doesn’t seem to be registering the short.

I assumed that the binding may be waiting for TRS to be pulled high but obviously connecting it to RTS as per the instructions is not achieving this.

What am I doing wrong??

@Kai you are listed as the author of the Serial Button binding. Do you have any ideas what may be wrong?
I assume you have this setup and working with your system, would you mind adding some additional detail as to what shorting pins 2 and 7 is supposed to do in terms of setting the voltage on the RTS line to see if there is a problem with my hardware or software or both!

So I got this working by just connecting everything to everything else to see if anything would work.
In the end what works for me is to short pin 2 and pin 4 (DTR)
Not sure why I have to use pin 4 vs pin 7 as it says in the binding readme but anyway it is working great for me now with this setup.
Hope this helps someone else. If you experience similar issues, please post here as I would like to know why my setup differs from the official instructions.