When you Zip the book only zip the contents of the folder not the top level folder. This is very important. If you don't the book will not process.
As shown above you zip
The pdf (optional)
Convert your text-searchable PDF into an XML file
Once you have a single PDF you are ready to make the special XML file that is used to search the book's contents. To convert your text-searchable PDF into this special XML file (LUNA uses the XML to enable text searching in the Viewer):