Worked example
A boutique proofs SHOP-4471 as a Code 128 internal shelf label; it cannot use that alphanumeric string as an EAN-13 for a distributor.
Before you print
Shopify’s Retail Barcode Labels app also uses Code 128; sales channels may require a GTIN. Export your product IDs to CSV if you need many labels.
Barcode artwork is not proof of an assigned GS1 number. A free barcode image and a GS1-issued GTIN are different things.