As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOI ON FLIGHT 2544- SMOKE AFT LAVATORY MESSAGE ILLUMINATED FOR LESS THAN ONE MINUTE AND WENT OFF. CHECKED WITH FLIGHT ATTENDENT, AURAL WARNING, NO SMOKE WAS DETECTED. REMOVED AND REPLACED APU. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.