Thanks to those who have replied to this topic.
After quite a few hours working with the resources and skill I have, I have found this task too difficult.
My pinouts and continuity testing seems fine. When I plug a train motor into the hub using the extension cable the motor does not operate.
I conclude that the connections are the problem, but I’m unsure of a solution.
It’s a pity, especially given that LEGO does not sell an extension cable and the third party product is not cost effective for me to purchase from Europe.
Has anyone else had success with producing a PoweredUp extension cable?