Enable Bulb as a shutter speed for tethered shooting from Capture One on iPad

I want to use the Bulb shutter speed setting on Capture One on my iPad Air to trigger my camera (Nikon Z9) when it is tethered via a cable. When I press the "shutter" in Capture One on the iPad, I hear it open the shutter on my Nikon Z9, but another click on the button doesn't close the shutter. Turning off the camera is the only way to close the shutter. I do light painting with variable shutter speeds for each exposure. Typically 50-100 exposures per finished image.