I received a credit at Kobo but trying to use it reminds me why I stopped buying there in the first place. Put book in cart, click checkout, apply discount, then it tells me I don't need to enter a payment method because the store credit covers the full amount. So far so good. There is then no way to actually complete the purchase. The "save and continue" button is grayed out and the only other link that works is back to the home page.
Guess they'll be keeping that $6.