The indicator's non-replaceable battery is dead. This happens after several years.
The pitcher still works. Manually replace the standard filter every 2 months (40 gallons) or the LONGLAST+ filter every 6 months (120 gallons). Track usage yourself.
IF THAT DIDN'T WORK: If the pitcher is new and the light never worked, the indicator may not have been activated. Open the fill lid for 5-8 seconds while filling the reservoir to the Max Fill line, then close it. The light should blink green.
HEADS UP: Filter performance is not certified after its rated life. Change it on schedule.