For security reasons, there are restrictions on how NX Credit can be spent. For example, items purchased with NX Credit cannot be sent to friends as gifts. Below you will find specific restrictions for Vindictus.
Hero's Lucky Box cannot be purchased with NX Credit until a character has reached level 70.
Channel and Server Megaphones can only be purchased with NX Prepaid with character level 70 or higher.
Guild Storage Expansion Coupons can only be purchased with NX Prepaid.