Amazon recommends obtaining a GTIN (product ID) - directly from GS1 or the product manufacturer for that exact reason. Here's a direct quote from their Seller Central help site:
"If you do not have a product ID for your product, you can request it from the manufacturer. If you manufacture the product yourself, visit the GS1 standards website for more information."*
According to a recent Amazon study, American small businesses sold more than 3.4 billion products through the online marketplace in the past year, up from 2.7 billion the previous year. Additional research underscores the importance of having U.P.C.s and GTINs in online product listings. A GS1 US study revealed in 2019 that the majority of growing small businesses (54%) said that using U.P.C.s in their product listings made it easier for customers to find and buy their products.
The reason retailers prefer GS1 over the alternatives is because your company is identified as the brand owner of that barcode and product in our global registry.