The unit has a tank built into the unit which must be emptied periodically. The front panel display will show STOP indicating that the water tank is full and needs to be emptied. The unit will not run until the tank is emptied. An alternate solution would be to use a hose to drain the unit automatically.
On models with a removable tank, if STOP remains after emptying the tank, remove the water reservoir and inspect the float switch for signs of debris or something that is not allowing the float to move smoothly. Additionally check the floatation material for indications the float is not acting as a float.
If you continue to have problems, please contact Haier Appliances at 1-877-337-3639 or visit https://www.haierappliances.com/support/schedule-service to arrange service.