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Guaranteed Free Book Downloads or a Prorated Refund

Every book promotion for free books comes with a Guaranteed number of downloads. If you don't get that guaranteed figure you get a prorated refund in store credit. If you buy a $100 slot and get 75% of the guaranteed free book downloads, then you get 25% of the money you spent ($25) as store credit

It's very unlikely you'll require a prorated refund

95% of limited time free book promotions hit the guaranteed figure or exceed it
90% of free in all stores book promotions hit the guaranteed figure or exceed it

In the rare case your book misses you get a prorated refund in store credit. The store credit never expires. You can use it with the same book or with another book