Why does KDP say content is outside the margins when nothing is there?

What KDP counts as outside the margins

KDP checks every object on the page, not only the text you can see. Its own list of causes includes invisible or blank elements, such as an empty text box or an art box. Page numbers and running headers must sit inside the margins too.

The inside margin, next to the spine, gets bigger as the book gets longer. It starts at 0.375 in for 24–150 pages and reaches 0.875 in for 701–828 pages.

Check the page size and bleed

The page size of your PDF must match the trim size you chose in setup. With bleed, add 0.125 in to the width and 0.25 in to the height, so a 6×9 book becomes 6.125 × 9.25 in. Bleed is all or nothing: if one page bleeds, the whole file must be set up with bleed.

How to fix the file

1. Set mirrored margins, with the inside margin taken from KDP's table for your page count.
2. Keep running headers and page numbers inside the margins.
3. Delete empty text boxes and stray objects, including hidden ones.
4. Embed every font fully.
5. Export a new PDF at your exact trim size, plus bleed if you use it, and check it in Print Previewer.

Other printers ask for more room

A file built to KDP's minimums can still fail elsewhere. IngramSpark recommends 0.5 in on all sides, plus a 0.125 in white strip on the bind side for perfect-bound and hardcover books. Lulu asks for a 0.50 in safety margin and a minimum 0.20 in gutter, and its 6×9 bleed page is 6.25 × 9.25 in.