Every EPUB file has to have a table of contents (toc.ncx) regardless of its topic. If you only have one entry in your table of contents (or the beginning of your book if it doesn't contain chapters), that makes your EPUB valid. However, if your book contains several chapters, all of them need to be added to the generated table of contents.
If you received the above error message from our review team, the problem with your table of contents is that it doesn't contain any entries: it only contains an incorrect 'cover' or 'start' tag. The editor you used probably knew that it had to create a table of contents but it created an incorrect one.
Two possible solutions:
1.
Open the book with Sigil.
Locate the toc.ncx and view with HTML view:
Change the content so that it reflects this example:
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The 'Book title' should be the title of your book, and the "content src" should point to the file where your book starts.
2.
Open the book with Sigil. In the menu, select 'Tools', then 'Edit Table of Contents'. Here, right-click on any element and choose 'Rename'. After you add the actual title of the book, "Start" changes to the title of the book and the Table of Contents will not be empty anymore.
Please only use this option if your book does not have chapters, for example with single short stories, magazines, comics or children's picture books, it works perfectly. Other text-heavy, longer format books need to have a full list of the chapters, otherwise some stores might reject them or open a quality issue case.
