Hi Jarno

Thank you for reaching out to us.

We have an option for you to set after what number of booked appointments customer will receive a coupon code. You would need to add a coupon placeholder into the email notification and then if you set 2 appointments, after customer books two appointments for the same service he will receive a coupon in the notification that he can use for the next booking. Since our coupons are not limited to the exact customers, that would mean that customer can also give that coupon to somebody else. 

Unfortunately it is not possible to sell coupons on Woocommerce. You can only manually send created coupons to your customers so they can use it for future bookings.

The only workaround that I can think of is to create a package that will have 0 as minimum required booking and maximum required bookings so customers can purchase that package without booking and then each customer that purchased a package you can send a coupon code like they have purchased a gift voucher. However, this is not a great workaround...