If a user knows the coupon code, then before clicking on a payment button he can enter it into the special field located under the list of subscriptions:

coupon code entry

 

For example, the coupon's settings are as follows:

coupon code settings

The coupon is not bound to any plan or a user, so it can be used for any plan and by any user.

 

Suppose, the user intends to buy a plan that costs $100. The coupon gives him a 10% discount. Therefore, if the user enters the coupon code when purchasing the subscription, the subscription will cost him $90:

using coupon code

 

User's subscription history:

using coupon effect