This problem has been resolved. Your cards should now work normally.
Due to a Vendor system connection issue, certain Nexon Game Cards are not correctly redeeming NX to their holder's accounts. Should you receive this error, please hold on to your game card. The card has not been invalidated and still holds the correct amount of NX. Once the error has been repaired, you may redeem your Nexon Game Cards as normal.
Thank you for your patience while we work to resolve this issue.