All products require a multipage INTERIOR PDF file, and a single page COVER PDF file.The Print API pulls information for printing from your platform, thus interior and cover files have to be specified with a URL from which Lulu can download the files. Dropbox is a popular file hosting platform utilized by many API users. Using encoded basic authentication in the URL is ok. All files processed by Lulu will be validated and normalized before sending them to production. If problems with the file occur, the order will be rejected or canceled and an error message will be displayed. Note: Please ensure that the URLs specified allow for the file to be downloaded.