I apologize if this has already been addressed. I skimmed through 100+ pages and may have missed something.
Initially, I thought the coupon was working OK since I did a test order. I have it set to take $10 off an order of $25 or more. However, I found out that it was giving the discount to anyone who used the coupon, no matter what their order total. I fixed that by changing the admin settings. I had it displaying the subtotal with discount applied. When I changed that, it no longer could be used for orders under $25. But if someone still puts in the coupon code when their order is below $25 it just takes them back to the same page where the coupon code is entered. There is no error message telling them they can't use the coupon.
I realize customers shouldn't be entering the coupon code if their order doesn't qualify, but I found out about the problem when a customer placed a $20 order and was given the $10 off. Is there a way to have an error show if they try to do this? Like...'Hey, you doofus...you can't use the coupon!' Just kidding on that one.