Selling with Amazon FBA means dealing with two different kinds of barcodes, and mixing them up is one of the most common reasons new sellers get stuck. Here is what each one does and how to get them.
Step 1: Get a product UPC to create your listing
Before anything ships to a fulfillment center, you need a listing. To create one for a new product, Amazon asks for a GTIN — almost always a UPC or EAN.
Buy one genuine UPC per product (and one per variation, such as each size or color). Enter it in the listing’s external product ID field.
Step 2: Let Amazon assign the FNSKU
Once your listing exists, Amazon generates an FNSKU — its own internal code that ties each physical unit to your account. You print these labels and apply them to your inventory before sending it in.
You do not buy FNSKU labels; they are free and created inside Seller Central when you set up a shipment.
Avoiding the most common rejection
The usual error is trying to use an FNSKU where a UPC is required, or reusing a UPC across different products. Keep it simple: one unique UPC per product for the listing, FNSKU for the warehouse units.
Make sure the UPC you use is genuine and has never been assigned to another product, or Amazon may flag a duplicate.
Frequently Asked Questions
Do I need a UPC for every variation?
Yes — each distinct variation (size, color, bundle) needs its own unique GTIN/UPC.
Can I sell on FBA without a UPC?
Sometimes, if you qualify for a GTIN exemption, but the simplest path for most products is a genuine UPC.
Is the FNSKU the same as a UPC?
No. The UPC identifies the product globally; the FNSKU identifies your specific units inside Amazon’s warehouse.
Starting with FBA? Grab genuine UPCs for your listings at GoodUPC — one per product, ready instantly.