if you have a product and have Barcode label just use the same number under barcode or if you don’t have then either buy from GS1 which is much expensive but buy if you are a brand owner of that product otherwise i recommend using this for your products which is cheap and reliable for you.
https://codesforamazon.com/product-category/barcodes/ean-numbers/
CategoryEAN UPC ISBN BARCODES
TagsEAN