We're sorry to hear you could not log in using our verification code system.
Our verification code system was probably initiated because the email address you used to try to make the purchase has been used previously to make a Leanpub purchase.
If you sign in to Leanpub here https://leanpub.com/login you will not need a verification code.
Here's how this works: we automatically create an account for you when you first purchase a Leanpub book, and we create a library for you at https://leanpub.com/user_dashboard/library. This is done so that you can always access the download links for latest version of all the books you get, all from one place.
If you've never set a password for your account, you can set a password here: https://leanpub.com/password_reset.
Once you are logged in, you can make a purchase as you normally would, without needing a verification code.