After the clients adds a service to their cart, they can add a discount code.
The client can click Have a promo code? found in the Review Your Purchase section.
The client can enter the discount code in the box, then click Apply.
The discount should be reflected in the order total.
* Clients can add one discount code to an order.
* Discounts can be applied to an entire order or specific services. Please see this article for more info on creating discounts.