Legal Question in Consumer Law in California

I think they must take it, but they do not have to refund anymoney to you.

You should read the terms and conditions of redeeming the coupon. I find it unlikely that any store would distribute a coupon that stated you can use it for anything in the store if it had items that costs less than value of the coupon. On the other hand, I guess somebody could have screwed up. In which case, you should probably be able redeem it for items that cost less the value of the coupon. As Mr. Marman stated, you still would not be entitled to any cash back.