As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 4201 FROM SAT TO DFW. DURING CLIMB, THE DOOR WARNING LIGHT CAME ON IN FLIGHT AND COULD NOT PRESSURIZED THE AIRCRAFT. AIR TURNBACK TO SAT AND LANDED WITHOUT INCIDENT. PERFORMED FORWARD ENTRY DOOR OPERATION AND INSPECTION, INSPECTED LATCHES AND LOCK CAM AND FOUND DOOR OPERATING NORMAL IAW MM 52-11-01. SYSTEM OPS CHECK GOOD AND AIRCRAFT RETURN TO SERVICE.