What’s your actual tx?
Anyway, the red led should work.
Also if it’s not working and the onboard rx is ok, you should be able to bind it.
As said plug it in, wait min 10 sec or better 20 to be safe it’s in bind mode. Then power up your tx with bind button pressed or whatever is the right way to do it with your tx.
If you set the FC to Spektrum 1024 and receiver mode to rx_serial before, it should work. If not, there might be a problem with the onboard rx.
Did you inspect it with a magnifier?
Maybe you can spot a loose leg or bad solder joint.
Also it’s always good to test the FC if it’s working before soldering stuff on it.
Should include that hint in my tutorial, but somehow I’m not able to edit it anymore.
Send a video to BG customer service showing that the red light isn’t working. If possible include a pic of your shipping label. Normally it isn’t a problem to get a replacement without sending the faulty one back.