The water flow through the XL-80 is right to left: the water flow on a standard tub is left to right. Try this: install the XL-80 backwards (sticker not facing you) turn on your spa and look for bubbles.
Turbo booster: If you are using a turbo booster with the XL-80 it may cause some interference with the venturi injector. Remove the turbo booster and install the Xl-80 as instructed.
If you are not using a turbo booster make sure the green light is on. If the green light is not on we recommend you contact Aqua Sun Ozone for further instruction.
The XL-80 does not work with tubs that install the ozone directly into a jet.