Hi,
I performed a test on your project. Please test the voltage at the following two places
1- GND and DIN.
2- GND and DOUT.
On the converter board. There is only one converter in the kit, right? We want to check if the problem is on the converter or on the screen board.
There is also a possibility that the 422 chip is interrupting the signal, so please disconnect the R622 and try it.
Hope it will help you.