Limit coupon use to three times?

You will have to add an extra row to the Users table in the DB. Something like coup_use.

Then when a coupon is used there will have to be an an if/else function applied to the Users table after you call it up in a SELECT * from Users recordset.

1. Check and see if the coupon has been used before.
2. If yes is it < 3.
3. if yes, the coupon gets an UPDATE applied and then is sent to the cart or checkout where they can see the discount.
4. If no, then you have to redirect to Sorry page that says Sorry, over the limit or something like that.

It might look something like this in theory.

if($coup_use != "") {
if($coup_use <3) {
echo header("Location: update.php")
} else {
echo header("Location: sorry.php")
}
}

The update page would just be code, something like SET Users.coup_use ++ and then redirect to cart or payoff page.

Also, make sure the coup_use table is set to NULL when users sign up for the first time.

There may be easier ways, but this is what I would do.

Hope you find it useful.
Jay