PX4 RC Ch8 no PWM servo output

My setup Taranis X9D+ and crossfire on a pixhawk PX4 using mavlink for control. All IN/OUT correct on Taranis. I can see the channel(RC CH 8 RC PASS THROUGH) in the radio calibration correctly and responding to control as well as the servo output responding to control inputs from TX but no servo output. all other channels are working except CH8.