Coupon code to appointments+ booking

So I've seen there was the same problem by another user over a year ago. Have you had enough requests to implement this that there is a way to add a coupon code to checkout upon booking an appointment?

I don't want people to have to sign up, etc. I want them to be able to come to the site, book an appointment, use coupon code, and check out.

Is this possible? How would I achieve it?