The complete manual fix

  1. Confirm whether you are supplying your own valid ISBN barcode or allowing KDP to place one. Do not include both.
  2. Download a new KDP template for the exact trim, binding, paper, and final page count, then identify its barcode location on the back panel.
  3. Move every word, logo, face, border, and important image detail out of that area. Preserve the clear background and quiet zone around a supplied barcode.
  4. If you supply the barcode, confirm the ISBN digits match this edition and keep the bars undistorted, uncropped, and on a readable light background.
  5. Flatten the production cover only at export; inspect the PDF at high zoom to ensure no hidden or transparent element crosses the barcode area.
  6. Compare the corrected cover against the current template and upload that unchanged file.

Keep the evidence

Save KDP's written notice, the unchanged exported file, the selected print settings, and the template used for comparison. Those records make a support case reproducible, and they are what the technical spec guarantee asks for.