Pixhawk 6x + Radiomaster Boxer +Radiomaster ERLS RP3 V2

Hi !!
I am a teacher and I am new to the field of drones. I am currently in a project with students.
The equipment we have:
pixhawk 6x + Radiomaster Boxer + ELRS RP3 V2.
I paired the radio with the ELRS RP3 receiver (The red light is fixed)
The receiver is plugged into the RC IN pins of the pixhawk controller.

Qground controller is installed and I connected to pixhawk…but the radio does not connect to pixhawk…
How to do ? Thank you for any help that would help me in advance

missing a wire… coz you need use a full uart.
Just check the following link
https://www.google.com/search?sca_esv=8315c933f3d307ba&sxsrf=ACQVn0_QBiYmhkjb2PsCYqpRLfu_UVAqfw:1707395535883&q=ELRS+RP3+wiring&tbm=isch&source=lnms&prmd=ivnbz&sa=X&ved=2ahUKEwjayaCD4JuEAxWo_rsIHSwAD2oQ0pQJegQIChAB&biw=360&bih=552&dpr=3#imgrc=_SqToapjxbAAWM

Hi! Thank you for your answer. There is no uart port to plug in the elrs rp3 receiver. According to the pixhawk 6x documentation, you must connect to the SBU/PPM receiver port: RC IN …

Your receiver have 4 pads… R is RX- T is TX - 5v is Voltage - G is Ground.

The RCIN pin its a timer input, CRSF/ELRS and SRXL2 require a true UART connection, so you need also change few parameters about your serial but i need investigate if elrs it’s supported by PX4