HorusX12S + PIXHAWK PX4 + QGROUNDCONTROL + UHF Transmitter and Receiver

Hello
I have Horus X12S + PIXHAWK PX4 + QGROUNDCONTROL + UHF Transmitter and Receiver
The UHF transmitter and receiver are connected. I have connected the receiver to the PIXHAWK RC IN.
But i get a blue led blinking slowly on the PIXHAWK. Can you help me get it work ?
Thanks