We're sorry the coupon link you're trying to use to make a purchase has expired.
If you found the link in one of our discount sale newsletters, you might find that the coupon is provided again in a future sale.
Also, you can try emailing the author(s) and asking for a new discount coupon, explaining that you were too late too redeem the coupon you found:
http://help.leanpub.com/en/articles/3852119-how-can-i-contact-a-leanpub-author