The book I want to buy is available in a number of formats. I did not find the option to select the desired format. Is it hidden somewhere? Does it come after checkout? Or do I pay once for all formats?

Thank you for contacting us. You pay once for all available formats. After you make a purchase, you should be taken to a web page where you will see all the available formats for download. You should also receive an email with download links for all formats, and you can download the formats any time from your Leanpub library.