As soon as I saw that 24% off code I hustled my way over to the shop to buy the monthly spawner I've had my greedy little eyes on. The price is down to $35, but with the coupon code checkout recognized the price going down to 26.60. Paypal...not so much. Paypal wants the full $35.00.
This happened to a friend of mine. With limited use coupons, there is a chance that the coupon will expire before your transaction will fully go through. PayPal doesn't catch it and update if the coupon expires mid-transaction.
This was me! I let Andrew know directly and he advised that the uses expire when there are X amount of completed payments with it, so if someone takes that last one while you're logging into PayPal and such then the coupon will fall off, you have to look purely at the final PayPal confirmation.
Make sure you look at the final price on PayPal check out. If the "last" coupon is used while your checking out, the price drop will fail for you.
