As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AT CRUISE ALTITUDE APU DETECTION INOPERATIVE LIGHT ILLUMINATED INTERMITTENTLY FOLLOWED BY APU FIRE LIGHT / BELL. FOUND APU INLET DUCT ACCESS DOOR COVER ON TOP OF FIRE LOOP. RE-INSTALLED DOOR COVER PER CMM 49-26-93 (AALA202107065301). REPLACED APU FIRE EXTINGUISHING BOTTLE PER AMM 26-22-01 (AALA202107070402).