When the Coupons add-on is enabled, a link "Have a discount coupon?" is provided at checkout.
Buyers can use this link to expand a section where they can enter their coupon code:
Provided that a valid coupon code is being used, the coupon will apply to the order:
The result will be reflected at checkout:
If an invalid coupon code is entered (for example, if the coupon code is misspelled, expired, or otherwise does not meet the coupon application conditions), the user will be informed of the problem.
For example, here is the result of using an expired coupon code:
