You can enter your Coupon Code on the checkout page. Click ‘Have a Coupon Code’ in the ‘Order Summary’ section, enter the Coupon Code, and click ‘Apply,’ as shown here. You will then see that amount deducted from the ‘Pay Now’ amount.
Please be sure to use your Coupon Code when you submit your reservation, since they cannot be applied retroactively or at the parking lot. Only one Coupon Code can be used per reservation, and Coupon Codes cannot be combined with any other offer or discount.