In order to activate one or more coupons you need to publish them.
You can publish a coupon by selecting Yes in the Published radio button while adding or editing a coupon. Alternatively, you can perform the following steps to publish an already existing coupon.
To publish a coupon:
1. Navigate to Components -> .Mighty Membership -> Coupons in the Joomla global menu. The Coupons page appears and displays the list of existing coupons.
2. Select the check box corresponding to the coupon you want to publish. Click the Publish button  in the toolbar, as shown in the following figure:
A tick mark appears under the published column.