Can't get LED feedback on generic flexi MIDI whatever I do.

[Mantras]

I am using a UC4 faderfox controller. The button I assigned works fine for it's function, it mutes the track 1 when I press it. But whatever I do, I won't get the script to send MIDI data to activate the LED.
I have the "Send value to device activated" but whatever I do the button LED just won't light up.
I tried the same button in Traktor 2 and it works great, so the issue is not the controller.