If your eBook has received rejection code 006, it means that a copyright notice or imprint is missing from the eBook file.

This is mandatory.

The copyright notice indicates who owns the rights to the work and protects your intellectual property.
The imprint/copyright notice is usually placed immediately after the title but can also be placed at the end of the eBook.

If your eBook has been given the rejection code 006, insert the copyright notice/imprint accordingly.
Check your eBook file and make sure the notice is displayed clearly.

If you have any further questions or queries about the copyright notice/imprint or any other aspect of eBook publishing, please contact our Customer Services team. We will help you to ensure that your eBook complies with the guidelines and can be successfully published.

More information about the imprint and an example can be found here