the safety sensors show a solid red light on one of them and the door won't close from the app

Diagnosis

The safety sensor beam is blocked or misaligned. One sensor has a solid red light (instead of green) indicating it's not seeing the beam from the other sensor.

How to Fix It

Realign the sensors on each side of the door track.

1. Check for and remove any dirt, spider webs, or obstructions directly in front of the sensor lenses.
2. Loosen the wing nuts on the sensor brackets just enough to move them.
3. Adjust the sensor with the solid red light until its indicator light turns solid green. Tighten the wing nuts.

If That Didn't Work

Direct sunlight flooding the sensor lens can also cause this, especially in the evening. Shade the sensor with your hand for a moment to test. If it turns green, you need to add a small sun shield (like a piece of electrical tape on the sides, not over the lens) or slightly re-angle the sensor.

Heads Up

Don't bypass this by taping over the sensors or trying to trick the system. The Meross app will still show a sensor fault and refuse to operate. This is a critical safety feature to prevent the door from closing on a person or pet.