Unable to calibrate ESC

I have a quad using Flame 60a ESCs and 3 of the ESCs calibrate correctly when I follow the All at once calibration instructions. The fourth one however continues to beep at an interval of one second, the manufacture’s documentation indicates that the possible cause of the one second beeps is “No output signal emitted from the throttle channel on the receiver”. Currently the ESCs are soldered to a Pixhawk 4 Power Module. Initially I had the ESC soldered to the servo 1 pads, but have since moved it to servo 8 as part of my troubleshooting efforts. I also updated the servo functions in Mission Planner setting SERVO1_FUNCTION to 0 and SERVO8_FUNCTION to 33. Any help/suggestions would be appreciated.

Small update: I measured the voltage of the signal wires for the 3 working ESCs and observed values between 1V and 1.3V. When I measure the voltage for any of the unused signal points I observe 35mV. When I measure the voltage for the signal wire that isn’t working I observe 2.3mV. I’m not sure why the voltage is so low.

Motor output wires to which output of the power module?
It is recommended to connect to the I/O PWM (Main1 to Main4) outputs.
Of course, according to the airframe model, you should read this pages:

Hi, I cannot even get one to recoginse throttle. can you post pictures of the wires you connect from esc to pixhawk?

hi @roomez , thank you for the response. I did have the cable connected to the I/O PWM. The problem is that something is wrong with the Pixhawk 4. Replacing the Pixhawk 4 resolved the issue.