As a way of promoting my books, I will often provide sample chapters at several websites. These sample chapters are free, of course. The purpose is to motivate people to visit Amazon.com to buy the complete books. I recently received an email from KDP and they are concerned that I may not have the right to publish my books at KDP. Apparently, the mere fact that samples of my books' content are published elsewhere on the web triggers a copyright dispute, Normally, if there is a genuine issue, someone has claimed to be the copyright holder and that my claim is false. As far as I know, no one has claimed that I violated their copyright. That being the case, I am not sure how to resolve the issue, or why there is an issue. It would be helpful if KDP would detail the exact cause of their concern.
What has happened is that a robot has matched text in your book against text freely available on the web. The main thing they're looking for is content that has been scraped from other sites and is being offered as original work.
You have to write them at the address they presumably provided and reassure them that you own the rights to your book.
I wish their robot would provide the link to the content it discovered. It is possible someone stole my content or quoted me. Without knowing what specifically ticked off the robot, it is hard to address the issue reasonably or intelligently.
Just cut and paste your book's text, or portions of it, and it will provide you with links where it found the text on the Internet.
If you let Amazon know that you gave away free chapters and assure them that you own the rights to the book, you should be ok to go. Don't make the mistake of not replying, because then they may delete your book without any further warning.