Once you have created your discount coupon, you can use the code in your marketing! (Steps to create coupons are here.)
Note: Discount coupons are presently only able to applied for pre-payment of consultations.
When a patient uses the online booking page, they have an option to enter in a discount code on the payment screen. They type in the coupon code and click on the "Apply Coupon" button which checks the validity of the coupon, and if ok, adjusts the amount to pay.