just a thought, but from your explanation it seems that the problem is you are only working on the lower chain. You already know the cargo mod you said, so you already know about the demand system there (however it might working 😉 )…
According to your description, you made a mine and a refine industry. But that’s just half the rent, because there is currently only one good in the game that is demanded from the cities.
Change your “goods-industry” so that it creates goods out of the ressource “refined copper”. Connect it to the chain and make a deliver system to the city in the 20 minute limit, and I’m sure it will be working.
I changed the cargomod into 3 different chains (all producing “goods” in the end though), and as long as a chain is complete, the industry starts producing.
Strange it works different in vanilla though, not sure why.