Diagnosis
First things to check: dead batteries or something blocking the IR signal. The remote uses infrared, so it needs a clear line of sight to the purifier's sensor.
How to Fix It
Replace the remote's batteries (they're typically CR2025 coin cells). Point the remote directly at the front panel sensor from no more than 15 feet away, with no obstructions.
If That Didn't Work
There might be interference from other IR sources like bright sunlight or LED lights. Try using the remote in a different room or with the lights dimmed. If it's still dead, the remote itself may have failed.
Heads Up
You can operate all functions from the control panel or the app, so the remote isn't strictly necessary, but it's convenient for bedside use.