When the cartridge inside device doesn't get wet it usually means that an airlock has formed in the water supply system, following steps will hopefully help you get rid of the problem entirely.
In order to check if that is in fact the case, we can suggest that you push the float through a little round hole located inside the device (the float stops the flow of water from the reservoir when the cartridge is wet enough).
Please, with some water in the reservoir, take the cartridge out of the device, and press the float. You can do this with something like a pen. Once you do this, the water in the square tub should rise up.
If the problem persist or you have more questions, please feel free to ask anything via our Contact form, we'll be glad to help you!