DIAGNOSIS That's the "Clean Filter" indicator. The unit has a sensor that tracks runtime, and after about 250 hours of use, it will flash "CL" to remind you to clean the air filter. It's not a fault, just a maintenance timer.
FIX Power the unit off. Pull out the washable foam air filter from the back grille. Rinse it under lukewarm water until it's clean, gently squeeze out excess water (don't wring it), and let it air dry completely. While it's drying, you can press and hold the "Filter Reset" button on the control panel for 3 seconds to clear the alert and run the unit temporarily without the filter. Once the filter is totally dry, put it back in.
IF THAT DIDN'T WORK If the "CL" light comes back immediately after resetting with a clean, dry filter, the reset button itself might be sticky or the control board's timer memory might be glitched. Try unplugging the unit for a full 5 minutes to let any residual power drain, then plug it back in and reset again.
HEADS UP Don't try to run the dehumidifier long-term without the filter. Dust and hair will clog the evaporator coil inside, making the unit work way harder and eventually leading to a different, much more expensive repair.