As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
TUS - FLIGHT 4218 - CREW RETURNED TO FIELD WHEN AFTER TAKEOFF RECEIVED AN AFT CARGO DOOR WARNING. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND THE DOOR NOT SECURE. THE DOOR WAS SECURED AND OPERATIONAL CHECKS WERE PERFORMED. OPERATIONAL CHEKS WERE GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.