There are three types of discounts that you can set up through your Instaproofs account: Sales, Coupon Codes, and Bounce-back Coupon Codes.
The sale option provides discounted pricing to all of your clients, while the coupon codes provide a discount to only those that you provide the code to. The bounce-back coupon codes are a special type of coupon codes that are explained in more detail here: Bounce-back Coupon Codes.
Since you are wanting to give the discount to just one specific person, you will want to create a coupon code for that person. Each of the coupon codes that you create will be unique, and your client will simply enter their provided code when checking out to receive their discount.
Here are a few articles covering each of the different coupon code options currently available in our system; click each article to learn how to set it up: