What is my actual shipping fee is more than the discount indicated by the promo code?

If your shipping fee before applying the promo code is greater than the discount, ShippingCart will still charge you the remaining amount.

For example: The shipping fee before applying the code is equal to USD16. You receive a promo code that entitles you to USD15 off your shipping fee. You will still need to pay a shipping fee amounting to USD1.