You may have received feedback from our review team that asked you to submit a document that we could use to confirm your exclusive publishing rights. This happens usually when we suspect a book might be PLR or the uploader may not hold the necessary rights.
To upload such a document, just go to your book's editing page by clicking on View and edit under the Books page. Under the Files section, you will see an "Options" button. By clicking on it, a few more options for file uploading will be revealed. Select that one "Acknowledgement of exclusive copyright" and upload your document in PDF format by clicking anywhere in the rectangle.