It was a mistake in my listing. It DOES NOT expire on the 21st. I mistyped and was supposed to put the 31st. If you look at the picture it clearly shows the 31st on the coupon. Thank you for bringing this to my attention.
Please read the comments a little further. The coupon is NOT expired. I typed in the date incorrectly. If you enlarge the photo of the coupon you will see that it expires on August 31, 2011 rather than the 21st. It was just a typo. Thanks.