If you have a promo code to use, simply load your cart and enter the promo code into the 'Coupon code' box under the item details. You'll see the coupon applied and the subtotal adjusted if successful.
Looking for a great deal? There's tonnes of affordable artwork waiting to be discovered here.
It's important to know that any discount or coupon applied to an order where your art is purchased will never affect your earning. All discounts are taken from Crated's share of the profit so you earn the same amount on the sale of an item regardless of discounts.