Amazon error 21: Inventory Loader - SKU not found in your inventoryAn Inventory Loader row references a SKU that does not exist in the account. Inventory Loader only adjusts existing offers; it cannot create products.How to fix error 21

Create the product first with a category flat file or Add a Product, then use Inventory Loader for quantity and price.

Compare your SKU column against a fresh 'All Listings' report - case and whitespace differences are the usual culprit.

If the SKU was recently deleted, allow processing to complete before re-using it.

Check you are uploading against the right marketplace - SKUs are per-marketplace.

All Amazon flat-file error codes