After a few time tinkering and testing the coupon management system, I found out that a woocommerce coupon must not contain uppercase letter, or else we'll get “Coupon does not exist!” error in cart/checkout page.
So here's a few suggestion:
1. Auto convert every letters to lowercase when a seller save the coupon.
2. Put a tooltip/text next to the coupon form to inform seller about using lowercase letter
3. Show a error warning “All letter in coupon code must be in lowercase” after a seller save his coupon (with uppercase letter).
Any of the above might reduce the error rate or even better might completely avoid this issue.
Ok, I found that the date is being pulled wrong and therefore the code wont work. When you chose a date to set the product coupon to expire it is entered as 4/30/2014. In the admin it has a red box and show that you need to correct it. when you select the date from the admin it changed it to 2014/4/30. The issue is the coupon code wont work b/c the dates are not the same. For me, when I changed the date in the admin, the code works fine regardless of caps or not. I think a coupon code should have the date required.
This should be a simple and quick fix of the code.
woocommerce uses hyphens between the dates in the admin 2014-04-30 and the sellers coupon page shows 4/30/2014. I am not sure if that matters but it is something else I have noticed. Along with that, if there is no date the code does not work at all, for me at least. I hope this is helping you guys come up with a solution.