You can redeem coupons in the in-game Settings menu.
Please see below for details on how to do so.
■ How to Redeem In-game Coupon
1. Tap the top right Menu button on the game screen.
2. Tap the Settings (Cog) button.
3. In the Info tab, tap Register Coupon and enter the coupon number.
■ How to Redeem Coupon Through the Website (PC)
1. Enter your Member Number and coupon number on the Register Coupon page.
※ Coupons can't be redeemed more than once.