On Friday I tried to publish the same book on Amazon KDP as a paperback and a Kindle eBook. The paperback went through review and was live that evening. The eBook never made it out of setup. KDP left it in Draft behind an error banner that does not identify a field.
The banner reads "Please fix the highlighted error(s) to continue." That is the entire message. Nothing on the page is highlighted. The eBook setup has three tabs, and KDP itself marks the first two as Complete. The pricing tab saves as a draft without complaint, with the exact data the publish button rejects a second later.
I checked the $3.99 price against KDP's band and confirmed the worldwide rights. Select was enrolled. The quality dashboard had zero items, and seven other titles were already live in both formats on this account. Retyping the price and switching Select off and back on changed nothing. I tried once more after the paperback went live. KDP returned the same banner.
Then I checked what the publish request returned. KDP's server rejected it with an empty errors object. The page had nothing it could point me to.
By the second day I was still rerunning the same failed publish. Nothing on the page had changed, and KDP still returned no field error, so I stopped trying to guess which field it wanted.
Today I wrote down the banner text, the empty error response, and which sections KDP had already marked Complete. I opened support chat with that in front of me. The first agent escalated it on the first touch.
I am keeping one part of this: check whether the system has named a field before I start changing fields. KDP named none, so I stopped guessing and handed support the response. The eBook is still in Draft while Amazon looks at it. The paperback is live with the same words.