No Throttle input from transmitter

Hardware: Tmotor Alpha 60a 12s ESC & MN-601S 170KV Motor, Pixhawk 4 autopilot and power management board, TBS Crossfire 8-ch diversity receiver, ix20 spektrum transmmeter
I am able to spin the motors when armed and have set the disarm PMW output so the motors are silent and don’t beep. after arming the drone, there is no throttle input. I cannot change the motor speed when moving the throttle up on my transmitter. There are 4 separate ESCs wired in 1,2,3,4 channels of PWM-out on the power management board. Each esc is connected to a motor and each esc is powered directly to two 6s batteries in series. I have set the PWM minimum and maximum output to its corresponding values (in esc documentation). Any idea on how to fix this problem? All help appreciated