Game Input MultipleXer

Wait so you said that you swapped RX/TX but it seems you have connected the RX from the Arduino to the RX of the USB-UART (i.e RX-RX and TX-TX?

The instructions seem to say that you must connect RX-TX and TX-RX. Did you try 'crossing' like that? It seems I'm looking at getting the same two components that you are which is why I bother to ask. Mind me if I'm misinformed, I'm new to these things and just kinda want some advice/help.

At first try Rx-Tx. If it did not work, you could try Rx - Rx (due to missing or wrong discription label on China cheap boards)

Using the same devices as OP, mine does work from RX-TX/TX-RX. I'm sure that RX-RX/TX-TX wouldn't work on this one. I'm sorted