QGroundControl Reverse Movement works with virtual joysticks, but not physical

I’m fairly new to all of this, but can’t find any help with the search…

I’m using QGroundControl to move a small ground robot for a project using a custom autopilot on custom hardware. When I drive with the virtual joystick, it seems to work fine. I recently got access to a UXVtechnology Navigator Tab3 and have been able to get the physical joystick working with QGroundControl, however, I can no longer go in reverse. Looking at the joystick support page ( Joystick Setup | QGC Guide (4.3) ) it would seem I need to enable “allow negative thrust”, but says “This mode is only enabled for vehicles that support negative thrust, such as Rover.” What do I need to add to my protocol to allow that? It seems odd to me that the virtual joysticks work as expected and this doesn’t.