Worked example
A merchant tests an internal carton reference CARTON-42 as Code 128. If Amazon supplies a separate FNSKU label for fulfillment, use Amazon’s own labeling workflow for that inventory.
Before you print
A self-made symbol does not substitute for a valid listing GTIN or an Amazon-generated fulfillment label. Check the current Seller Central instructions.
Barcode artwork is not proof of an assigned GS1 number. A free barcode image and a GS1-issued GTIN are different things.