all i know about korean nexon cash is :
-you can pay it : By phone (gotta be in korea)
By Nexon Card Cash available in Family Mart (sort of korean seven eleven).. i saw one on the net and it looks like a telephonic card with a code on it. (i know how to validate that code if someone is intersted)
/!\ You need to have a account with a confirmed or an old KSSN .. if you didnt use a kssn to do ur account that lmean that you need to confirm it with a kssn(like i did) if you want to put valid nexon cash on ur account
My tip : get a korean friend in warrock and ask him after if he can make a nexon gift(this is the new nexon option , you can make a gift
) to you since you cnt have one.. try it it worked 4 me.