Configuring Pixhawk 4 PWM AUX Outputs for Gimbaled Camera

My team and I are setting up a Foxtech FH310Z gimbaled camera on a Holybro PX4 for a quadcopter-x via the PWM/IO breakout port, using MAIN channels 5 - 8 (AUX Channels 3 & 4) for the gimbal and camera controls. Main channels 5 and 6 (AUX Channels 1 & 2) work without any problem for panning and tilting the gimbaled camera, but we get no response from the 7th and 8th main channels for zoom and triggering the photo/video capture.

What are we overlooking? Any help would be greatly appreciated.