DIAGNOSIS That E1 code means the machine thinks its water tank is full, even if you just emptied it. It's almost always a sensor or float issue, not actual water.
FIX First, power the unit off and unplug it. Pull the tank out and look inside for the little white float, usually on the side. Gently lift that float up and down a few times to make sure it's not stuck in the down position. While you're at it, check that the tank is sitting perfectly level on the base when you slide it back in. A slight tilt can mess with the sensor. Plug it back in and turn it on.
IF THAT DIDN'T WORK If the E1 is still flashing, the tank sensor on the base might be dirty or obstructed. With the unit unplugged, get a cotton swab and some rubbing alcohol and gently clean the little plastic sensor posts where the tank sits. Let it dry completely before plugging it back in.
HEADS UP This sensor is super sensitive. Make sure the tank is completely dry on the outside and there's no debris like a dust bunny blocking the float's path before you reinstall it.