You can use a coupon in either of the following two ways:
① In-Game
Go to Settings → Account → Enter Code
Enter your coupon code, and the reward will be delivered to your in-game mailbox.
② Web: https://coupon.outerplane.vagames.co.kr/coupon
Access the coupon redemption page via the link below, then enter your UID, Server, and Code.
👉 Coupon Page: