Set CC23 to zero, that might turn it off. You may need to look at the plugin's manual to determine it's MIDI implementation.

There is no such thing as "Off" or "On" in MIDI CC messages themselves, only in how the synth responds to that CC message. CC messages output a range of numbers, usually from 0 to 127, and the synth itself determines what that means. In some synths 0 might be off and 127 might be on, in others it might be the opposite (I know of some synths where the sustain control is 0 to sustain and 127 to not sustain where in others it's the opposite), in some 64 might be off while 0 and 127 might be on (for example with an EQ control where you can boost or cut a frequency), and some synths might use all 3 for different parameters.

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