Amazon cannot list an offer without a product identifier. Items with no ISBN are left out of your files (the generator tells you how many), and items whose ISBN matches several Amazon catalogue entries (common with reprints and editions that share an ISBN) can be rejected with confusing errors. The fix for both is the same: assign the exact ASIN, the identifier of the specific Amazon catalogue page you mean.
Where to get ASINs
- Items already listed on Amazon (for example through another service): run an Active Listings Report in that marketplace's Seller Central under Reports » Inventory Reports. It contains every SKU with its ASIN.
- Anything else: search the Amazon site for the ISBN or title, open the correct edition's product page, and take the ASIN from the URL (the code after /dp/).
For books, the ASIN is often the ISBN-10 itself. That is normal; use it as the ASIN.
Assigning them
On the Amazon Files page, open Assign ASINs. Either upload the Active Listings Report file directly (the SKU and ASIN columns are detected automatically), or paste pairs, one per line:
102236, B000ABC123
102237, 0714842850
The tool reports how many items were updated, how many kept an existing ASIN (tick Overwrite to replace those), and any SKUs it could not find in your inventory.
After assigning
Regenerate your file. Assigned items are included from then on, pinned to the exact catalogue page you chose. If an affected listing is already stuck in an error state on Amazon, delete that SKU in Seller Central first, wait for it to clear (up to 24 hours), then upload the fresh file.