[Kiwiburger]

Did a quick google and the very first sentence I read is this: "This stereo pedal is equipped with a Minimum Volume knob and a battery strength LED. ..." You realise you might need to turn the knob down?

I even wonder if it's actually an expression pedal at all. They call it a CV pedal and talk about it "sending a signal" from output 2. That sounds suspiciously like it's intended to drive real analog voltage controlled synths ... the manual is a bit unclear what they mean.

If you getting a volume change without running the audio through the pedal, you must already have it working as an expression pedal. Turn the minimum volume knob off (counter clockwise) and then dive into synth programming to make it do what you want.

It's basically a stereo volume control primarily - so you have two inputs and two outputs, and it controls the level of both via the VCA amps. If you want to use it as a CV you have to set the switch to CV, and use the output #2 to connect to your synth. If it's actually an expression controller, you will need to use TRS.

Good luck.