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The default coupon system supports setting a single coupon code for any promotion. If set, a matching coupon code must be supplied for the order, or the promotion is not applied.

## Interfaces

To change the default implementation, implement the interfaces below, and register them as the default services in the service locator. See [Dependency injection in CMS](🔗) for more information.

### Add coupons to an order

An order's coupons can be accessed via EPiServer.Commerce.Order.IOrderForm.CouponCodes. This is an ICollection<string>, which supports adding and removing coupon codes.

#### ICouponFilter

Components mentioned here are available in the EPiServer.Commerce.Marketing namespace.

This interface has one method that has to be implemented. The method filters out promotions that do not meet the requirements for coupons. The method should return a PromotionFilterContext, where the IncludedPromotions property contains all promotions that are still valid after coupons are evaluated. It should also populate the PromotionCouponCodeMap property with information about applied coupon codes, and add descriptions to ExcludedPromotionDescriptions for any promotions that were excluded.

  • filterContext – Its IncludedPromotions property contains the list of promotions that the engine will evaluate against the current order.

  • couponCodes – The list of coupon codes supplied for the order.

  • PromotionFilterContext.IncludedItems – It should include all promotions that meet the coupon requirements. Two types of promotions are included: those that require a coupon and provide a valid one, and those that do not require a coupon. Eliminate promotions that require a coupon but no valid one is supplied.

Here is an example of a filter that verifies against a single coupon code.

### ICouponUsage

Implementing this is optional, but you must do so if you want to track coupon codes that have been used. Only one method has to be implemented.

This method is called when a cart is saved as a purchase order. It is supplied with one parameter: a list of any promotions (both with and without coupon codes) that were applied to the purchase order. Here is an example of implementing it.