As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN PRESS RELIEF MESSAGE CAME ON. SHORTLY AFTER UNABLE TO MAINTAIN PRESSURE, SO PROCEEDED WITH AN EMERGENCY DESCENT UNTIL LEVELED AT 20K AND CABIN MAINTAINED 10K. MX FOUND INSULATION AND DEBRIS IN OUT FLOW VALVE. VALVE CLEARED AND PLACED ON MEL 21-34-1. REF DMI 7743, MEL 21-34-1: REMOVED AND REPLACED UPPER CABIN PRESS RELIEF VALVE ASSY IAW 21-34-01. DMI 7743 MEL 21-34-1 CLEARED. AIRCRAFT OK FOR SERVICE.