We use [login to view URL] as a source for our site and have a events plugin that has a coupon option. We can make coupon and it works but coupon can be used over and over with no limit to a number of times used in
total or the number of times used per user.
-- make it so we can limit total number of coupon uses
-- make it so can limit number of times a single user can use the coupon
Make small PHP edit to limit use of coupon code to 1 per user