Coupons feel like a scam

I placed an order because I got a $10 off coupon. The final showed $10 less when I placed the order and when I paid it showed the full price. When I asked them about it, they said that at the first time the order didn't go through and the coupon takes 24 hours to show up again. So I paid full price despite seeing the total that is lower and I can't do anything about it.