D810 tethering problem

[David Mitchell]

Hi folks,
I am trying to set up my old D810 for tethering to my Mac Pro. I cannot seem to have ever been able to have the computer detect the camera via USB, either directly or through Lightroom.
I am unsure if this is a problem with the camera connection point or something else.
I have tried everything, updated the D810 firmware, restarted everything, tried different ports and cables to the computer etc etc.
I want to buy a good quality tether cable but they are expensive and I should be able to at least test it out by the supplied cable.
Also, I can only import images via a card reader. I have never been able to download them by connecting the camera. maybe that is a related problem.
I was hoping that someone else may have had the same problem in the past and found an easy fix.
FYI, when I connect the camera with a cable, go to Lightroom (CC), go file, tethered capture etc, the box just tells me that the camera is not detected.
Any advice is much appreciated.
Regards,
Dave,