DIAGNOSIS That's the dishwasher telling you the door isn't latched properly. It's a super common sensor issue on this model—the machine thinks it's still open even when it looks closed.
FIX First, check for any obvious obstruction like a utensil or dish rack blocking the door. If it's clear, open the door fully, then give it a firm, decisive close—you should hear a solid click. If that doesn't work, unplug the dishwasher for 60 seconds to reset the control board, then try again.
IF THAT DIDN'T WORK The door latch switch itself might be faulty. You'll need to check the switch assembly (located on the door frame near the latch) for damage or a failed connection. Replacing that switch is a pretty straightforward DIY job.
HEADS UP Don't just keep slamming the door. If the issue is a misaligned latch, forcing it can bend the strike plate and make the problem permanent until it's physically realigned.