@substancev For Matricom G-Pad BX (Bluetooth).. I added the following line to ~/udev/rules.d/99-bluetooth.rules:

SUBSYSTEM=="input", ATTRS{name}=="Bluetooth Gamepad", MODE="0666", ENV{ID_INPUT_JOYSTICK}="1"

I got this line from a RetroPie setup. The menu system allows to add bluetooth devices to the udev rules. I copied this rule and added manually.

I guess the question now is: How do I know how to manually create this file?

I hope this helps anyone with a Matricom trying to use Recalbox.