FNSKU is a specific amazon only barcode. GTIN and UPC barcodes are worldwide.
GTIN Stands for: Global Trade Item NumbersUPC Stands for: A UPC is a standard product identifier to help you sell your product.
How are they different? UPC is a type of GTIN, containing 12 digits.
You need either the UPC or GTIN to create the listing on Amazon. This should be purchased via Gs1, OR you can apply to amazon for a GTIN exemption.
The type of Barcode that is specific for amazon is called an FNSKU (Fulfilment Network Stock Keeping Unit). This is the label you would want to go on each individual unit.
You do not put your UPC on each unit - Just the FNSKU.