You need to have NPoints on your character. Then, you need to log on KO website, go to your account and do something called "SMS Verification":
(1) You click in Verify;
(2) Then it's required that you write your cellphone number;
(3) After you do this, you will receive a code thought a text message into your cellphone;
(4) Then you come back to the website and insert the code that was given to you.
(5) After all of this, you will be able to trade and merchant in-game.