How to connect R81 receiver to Pixhawk 6X?

R81 wiring to Pixhawk 6X, how can I do it? I have attached the wiring for the pixhawk 6x (and the ground board of it not sure what its name is). However, if you look in the image, the Receiver should be connected to RCIN but there are only 4 RCIN inputs and they are connected to the arms. In the wiring diagram on the official website, they do not show what I can connect it to and left unconnected! (all in one receiver, I assume)

Any idea?