Why are my Wix Online Store coupon codes not working?
If you created an Online Store before January 24th, 2013, your Shopping Cart may not support the new coupon feature. To use coupons, please delete your old shopping cart and checkout button and add the Shopping Cart again.
To add the Shopping Cart: From the left side of the Editor, click the Add icon > click Online Store > click Shopping Cart.
Once your customer adds an item to the cart they will then see the option to add a coupon. They should click on Apply to activate the coupon.