As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOI - FLIGHT 2364 - THE FLIGHT RETURNED TO FIELD WHEN DURING THE CLIMB, THE CREW RECEIVED A FUSELAGE DOOR WARNING FOR THE REAR CARGO DOOR. MAINTENANCE INSPECTED THE DOOR AND FOUND THE HANDLE IN THE UNLATCHED POSITION. THE HANDLE WAS SECURED AND OPERATIONAL CHECKS WERE PERFORMED. ALL CHECKS WERE GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.