What was found
EN ROUTE MSY TO CLT - AFTER TAKEOFF, THE LANDING GEAR INDICATES DOWN AFTER THE LANDING GEAR LEVER WAS MOVED UP. UPON ARRIVAL, THE LANDING GEAR HAD AMBER -X- INDICATIONS ON THE WHEEL PAGE. MAINTENANCE REPLACED THE LEFT MAIN LANDING GEAR EXTENSION PROX SENSOR, FIN 23GA. OPERATIONALLY CHECKS OK.