First upload (epub)
The book upload panel only accepts epub (ebook format) files.
If you don't have an epub file, read this article.
Subsequent uploads (epub)
Ebook validation is an internationally approved process of checking the code within the books to make sure that they display well on all kinds of devices. The ebook stores only accept "valid" ebooks: your book might look OK on your computer and doesn't work on another device. Ebook validation is here to make sure that all books work on all devices correctly.
When you re-upload a book, you can immediately see validation results: this is to make sure that nobody accidentally overwrites a right file with an invalid file. As we automatically send your changes to the stores, your re-uploaded ebook file must be perfect. Solutions of most common validation errors can be found here, but we're more than happy to help if you get stuck.
The cover image should be a jpg or png file and at least 800 x 1280 pixels.