Before Uploading Your Ebook:
In Sigil, right-click on the cover image to specify that it’s the cover.
Update the metadata on file title and author name.
Make sure you’ve set up the table of contents and contents page.
Do IDPF validation to check for errors: https://www.ebookit.com/tools/bp/Bo/eBookIt/epub-validator You want ZERO errors.
Time to upload: