Diagnosis
Yeah, that red light is the filter replacement indicator. The unit locks out to prevent you from running it with a spent filter, which is common after about 6-12 months of use.
How to Fix It
First, confirm you've installed a genuine Rabbit Air replacement filter correctly. Then, press and hold the "Filter Reset" button on the control panel for 5 seconds until the red light turns off. The purifier should start up normally.
If That Didn't Work
If the red light persists, unplug the unit for a full minute, then plug it back in and try the reset procedure again. Sometimes the system just needs a hard reboot.
Heads Up
Using off-brand filters can sometimes trigger this error even if the filter is new, so stick with Rabbit Air's own replacements to avoid hassle.