As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED APU OIL PRESSURE CAUTION MESSAGE IN FLIGHT EN ROUTE FROM CLT TO MGM. CREW SHUT DOWN APU PER QRH, RETURNED TO CLT AND LANDED WITHOUT INCIDENT. MAINTENANCE TROUBLESHOT APU, REMOVED AND REPLACED APU LOP (LOW OIL PRESSURE) SWITCH AND PERFORMED CHECKS USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT RELEASED FOR SERVICE.