"You do not have permission to use this coupon"

I got this message when trying to apply the code from the mail "Special Limited Time Coupon! -15% OFF.

I am trying to buy Longing Dream by DM and RPublishing, price $9.97 and "You Cant Deny Me dforce for Genesis 8 & 8.1 Female(s) by fefecoolyellow, price $ 7.97. The sum is $17.94. Both products say that they are eligible for coupons and the coupon expires tonight.

What is the problem?