Vantec Speed controller with Vex

I just got my Vantec RDFR23 speed controller with a set of NPC 12/24 volt motors. Unfortunately it doesn’t seem to want to work with my Vex controller.

I thought I read something on the vex website about a small piece of hardware that may be needed for the vex controller to work with other speed controllers. I can’t seem that info now.

The Vantec controller accepts servo wires but ignores the red wire (it’s cut on the speed controller side)

Thanks for any tips,