Coupon codes may only be valid on certain products. They will not be valid on new launches, products which are already discounted as part of a sale or promotion, this includes Build Your Own Sets and some site promotions. This may be the reason why your discount is not being applied.
This does not apply to coupon codes exchanged from Huda's VIPs Rewards, these should be applicable even on sale items (subject to change).
If you've used a Huda's VIP Reward code that cannot be redeemed, please check if the code has been entered correctly then send us a screenshot of the error you have received and details of your code so we can check this for you.
We are unable to process refunds for promo codes that have not been successfully redeemed on an order at checkout, however, you can always use your code on your next order (as long as these are still within the validity period).