Reaction based on a device parameter's current value

Hi. I'm new to CSS. I am trying to add a reaction so that whenever my selected track's selected device has a change in parameter 17, it reads the new value and does something conditionally based on that. I have a VST where some of its parameters have been "configured", so that "Model" is parameter 17, and it has several types: Multimode, Cascade, Ladder, BITE, etc.

I want to send a different LED colour to the control based on the value.

The problem is, I can't even get a listener to fire a log message when the device's parameter 17 is changed. I even tried parameter 1, nothing.

These are the things I'm using:

Device Parameter's value value has changed
----> self.song().appointed_device.parameters[16].add_value_listener

do this....

self.show_message(str("Selected track blue hand selected device parameter 17 changed"))

And do this...

self.log_message(str(self.song().appointed_device.parameters[16].value))

But no matter what I do, neither the log.txt line nor the status line messages fire. I have tried this out with something simpler like selected track's SOLO status changed, and those work. I can't figure out how to get it to react to a change in the value of the parameter. Isn't that what add_value_listener does?