Diagnosis
That's a door error. The machine can't detect that the door is properly closed and locked. Usually, the door latch assembly is faulty or something is blocking the door seal.
How to Fix It
First, power the machine off at the wall for 2 minutes. Open and firmly close the door. Listen for the lock click. Power back on. If DE returns, inspect the rubber door gasket. Remove any coins, hair ties, or debris lodged in the fold.
If That Didn't Work
The door lock/latch assembly itself likely failed. It's a single unit (part # 5220ER2002A). You must unplug the washer, remove the top panel, and disconnect the old latch to replace it.
Heads Up
Never force the door closed. If the latch is broken, forcing it can damage the strike plate on the door itself, which is a much bigger repair.