FNSKU

The FNSKU (Fulfillment Network SKU) is the barcode FBA uses to route and attribute inventory. Unlike a manufacturer's UPC — shared by every seller of the same product — an FNSKU is yours alone: units labeled with it are credited to your offer and never mingled with anyone else's.

The alternative, stickerless commingling on the manufacturer barcode, saves labeling cost and adds someone-else's-counterfeit risk. For private-label brands the answer is nearly automatic: FNSKU everything. Print them from Seller Central, put them on at the factory (not the prep center), and make label accuracy part of the pre-shipment QC checklist — mislabeled inbound is a receiving nightmare with fees attached.