Cheap Flights from Phnom Penh (PNH) to Taipei (TPE) from $341

The service on the plane was excellent. My only issue with this flight was that there was no way to upgrade. We would have gladly paid to upgrade to premium economy or even business class and there were MANY empty seats in both. I tried doing it online, asking at check-in and even asking at the gate but nobody seemed to have the ability to help us. Online I received a message that the upgrade was not available because the flight was full but that was not the case at all.