For some purchases (such as Shelf spots), we let authors apply some of their unpaid royalties towards a discount for the purchase.
When unpaid royalties are used in this way, the discounted amount does not involve a payment from the author to Leanpub. Rather, it is just a discount.
The applied discount may be for up to 100% of the purchase.
If the discount is for less than 100% of the purchase, then you will pay for the non-discounted portion of the purchase using our payment checkout process. That payment will have any applicable sales taxes added to it, which will be shown on the checkout form.