If you friend files a fraud claim, then it is possible to get your nexon account banned.
However, you can create a paypal account yourself and have your friend send you the money that he owes you as gift or for services
If you are still paranoid, you can also tell him to make a statement saying that he will not chargeback or he has already received the items.
Also, you might have to link your bank account or a credit card if you want to make any purchases.