I seem to be having an issue with creating and managing promotional coupon codes. I have created the promotion to use a percentage to be applied to the order subtotal, I have also set the date range that the promotion would be valid. I have even tried setting the promotion for different customer roles, but nothing seems to help. Whenever I attempt to use the promotion as a test it simply tells me that the coupon code cannot be applied with no further explanation. Is there any way to fix this issue?