Diagnosis
The continuous red light means the ice maker can't detect that it has enough water in the tank. This is almost always a sensor issue, not an actual water shortage.
How to Fix It
First, unplug the unit and remove the water reservoir. Turn it over and check the two small metal sensor probes on the bottom—they get coated in mineral deposits. Scrub them gently with a vinegar-dipped cotton swab or toothbrush to clean them. Refill the reservoir, plug the unit back in, and it should switch to a solid green light and start working.
If That Didn't Work
It could be the reservoir isn't seating properly. Check that the black rubber gasket around the opening is intact and seated correctly. While the unit is unplugged, firmly press the reservoir into place until you hear a distinct click on both sides.
Heads Up
Never run it without the reservoir fully clicked in, as that can trigger an error and damage the water pump. Always use the handle to lower it, don't just drop it in.