Redeem a one-time UD code in your profile settings. Its fixed amount is added to your account once, and the redemption appears in your history. This is separate from a percentage promo code entered during payment: that code adds bonus UD to a paid order. If your code is rejected or credit is delayed, contact support and keep the code until the issue is resolved.
How one-time UD codes work
Redeem a fixed-value code in profile settings to add UD to your account once.