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