Product identifier
A product identifier is any standardized code that uniquely identifies a product to a channel, primarily the GTIN, the brand plus MPN combination, or the brand on its own for certain categories.
Channels need a way to know exactly which product a listing refers to, so they can match it against other sellers, pull in extra information, and verify it is a real product. The accepted identifiers are the GTIN (the universal barcode), the brand combined with the manufacturer's MPN, and in some categories the brand by itself.
They matter because correct identifiers usually mean broader reach and better matching, while missing or invalid ones are a leading cause of disapprovals. Most branded products are expected to carry at least one valid identifier; the channel uses it to connect your listing to the wider product graph.
In the feed, identifiers live in their respective attributes (gtin, mpn, brand). When a product genuinely has none, you declare that with identifier_exists set to 'no' rather than leaving the channel to guess. The rule is simple: supply real identifiers when they exist, and only flag their absence when it is true.
MartechFlow validates the identifier picture per product: checking that a usable GTIN or brand-plus-MPN is present and well-formed, and flagging rows that lack a valid identifier so you can supply it or correctly mark identifier_exists before export.