As far as I understand, the latest versions of the plugin (3.x.x) don't work with the latest versions of OBS Studio (31.1.2): "listening" is enabled and work, and the parameters can be set, but the corresponding actions don't occur.
As a solution, you can use version 2.3.0 — at least in my testing, the actions started to execute immediately (tested with the M-Wave SMC-Mixer MIDI device). The interface is different, but the essence is the same.
I hope the author is waiting for the release of OBS 32 to update their plugin's compatibility to that version immediately.