Of all the cover rejections, this is the most mechanical: two numbers that were supposed to be identical aren’t. One number lives in your title setup (the ISBN you typed or were assigned). The other lives inside the barcode graphic on your back cover, encoded in the bars themselves. KDP’s system reads both — and when they differ, manufacturing stops, because a book whose barcode rings up as a different ISBN is a logistics error Amazon will not ship.
What KDP is actually saying
KDP’s published barcode rules are precise. If your barcode includes an ISBN, it must be a valid ISBN and it “must match your book’s ISBN exactly.” If the barcode carries a price add-on, the price code should match your list price. And if KDP’s automated system can’t scan your barcode at all, that alone is a validation error — unreadable barcodes “will cause delays and issues during manufacturing.” The full spec for a barcode you supply yourself:
| Requirement | KDP’s published spec |
|---|---|
| ISBN in the barcode | Valid ISBN-13, matching the book’s metadata ISBN exactly |
| Size | Suggested 2″ × 1.2″ (50.8 × 30.5 mm); minimum 1.4″ × 0.8″ |
| Color | 100% black bars — not RGB, not CMYK, not registration black — on a solid white background |
| Quality | Vector preferred; raster barcodes at 300 PPI, sharp and square to the cover |
| Placement | At least 0.25″ (6 mm) from the spine and from the trim edge; must not overlap any text |
| No barcode supplied? | KDP places its own ISBN barcode in a 2″ × 1.2″ white box, lower-right corner of the back cover |
The usual causes, in order of how often we see them: (1) the barcode was generated from a different ISBN than the one in the metadata — an earlier draft’s free KDP ISBN, or the ISBN of another format (paperback, hardcover, and ebook editions each carry distinct ISBNs, and KDP’s own guidelines ask that an ISBN, if printed on the copyright page, match the barcode’s); (2) the metadata ISBN was typed with a digit wrong — KDP’s ISBN help page recommends copying and pasting the number from your ISBN agency record precisely to avoid mismatch errors; (3) the barcode encodes an ISBN-10 while the metadata holds the ISBN-13 (or the reverse); (4) the barcode is fine but unscannable — blurry, shrunk below the minimum size, printed in color, or flattened into the cover art as one image, which KDP also prohibits.
Check it yourself
- Decode your own barcode. Any free barcode-scanner app or online ISBN decoder reads the number out of the bars. Compare it character by character with the ISBN on your Paperback Content page — not with the number you meant to use.
- Check the check digit. The last digit of an ISBN-13 is a checksum. If your decoded number’s final digit differs from the metadata, the barcode was generated from a mistyped number, not merely mislabeled.
- Measure the printed barcode. In your cover PDF it should sit near 2″ × 1.2″, at least 0.25″ clear of spine and trim, over plain white — not over art, and not overlapping text.
- Check the ink. Barcode bars must be 100% black. A barcode that looks black on screen but was built in RGB or registration black can fail the scan.
Barcode math not your idea of fun? The free check reads your cover the way KDP’s system does — barcode zone, ISBN consistency, spine, margins, fonts — and reports every problem in plain English within 48 hours. Get the free check →
How to fix it
The zero-risk fix: let KDP place it
Remove the barcode from your cover file entirely, leave the lower-right 2″ × 1.2″ of the back cover empty, and KDP prints its own barcode — generated from the very ISBN in your metadata, so a mismatch is impossible by construction. This is what our own build engine does: the barcode zone stays clear and Amazon handles the rest. It’s the right choice unless you specifically need your own barcode (for example, one carrying your own ISBN with a price add-on).
If you keep your own barcode
Regenerate it from the exact ISBN-13 string in your metadata — paste the number, never retype it. Export it as a vector (or 300 PPI raster), 100% black on white, sized at 2″ × 1.2″, placed clear of the spine, trim, and any text. If you include a price add-on (the small EAN-5), set it to your actual list price. Then decode the finished cover PDF once more before uploading — the check takes thirty seconds on the file you’re actually submitting, which is the only version that matters.
If the metadata is what’s wrong
Fix the ISBN in the title setup instead — but know the limit: once a book is published, its ISBN is locked to that edition. A wrong ISBN discovered after publication means a new edition, not an edit.
The honest limit
A matching, scannable barcode passes this check — it doesn’t validate anything else about the number. If the ISBN itself was assigned to a different title or format at your agency, the barcode and metadata can agree perfectly and the book is still mis-registered upstream. Verify the assignment at your ISBN agency (in the US, Bowker) if the number has any history. And if your cover art has anything important sitting in that lower-right corner, KDP’s placed barcode will cover it in print whether you supplied your own or not — design the back cover around the zone from the start.
Or send us the files — the check is free
Email your interior and cover PDFs and we'll tell you exactly what's wrong — in plain English, free, within 48 hours. If it does need fixing, the by-hand fix is $19 and we redo it free if KDP rejects it for a formatting issue we were hired to fix. We rebuild files to be compliant with KDP's published spec — that's the promise we can keep.
Prefer the whole library in one file? The KDP Rejection Field Guide (free PDF) collects every guide, table, and the 13-point checklist.
More from the Help Library
- The KDP & IngramSpark Help Library — all guides & tools
- ISBN & barcode rules — who provides it, where it goes, what must match
- IngramSpark barcode placement — the 1.75 × 1″ zone
- Cover file has multiple pages — the one-page rule
- Spine width calculator — KDP and IngramSpark math
- Page size does not match the trim size you selected
- The free rejection check — all 13 checks at once