limit on coupon use?

Where did the coupon come from?

The problem with some online coupons is that someone gets the coupon
code (or scans a physical coupon) and posts in on the Internet. Then,
the coupon gets used be dozens or even hundreds of people. To prevent
this, they'll sometimes uniquely code the coupon such that it can be
used only once.

Now, you'd think that they'd be happy to have as many people as
possible buy from them with coupons. But there are all sorts of
reasons to restrict coupon use, including getting information on
markets.

I assume you received a flyer and entered the coupon code only once.
If that's the case, then it sounds like they made a mistake and owe
you $5.

I just think if they do not want people to use the same coupons all
the time, then they should not advertise them all the time. Maybe
they ought to switch it up.

Then they should accept it.
They should get a new one as well if they are tracking them.