GTIN
A GTIN (Global Trade Item Number) is the globally unique product barcode number, such as a 12-digit UPC or 13-digit EAN, that identifies a specific product everywhere it is sold.
GTIN is the umbrella term for the standard retail barcode numbers: UPC in North America, EAN in Europe, JAN in Japan, and ISBN for books. Whatever the regional name, the GTIN ties your listing to a real, manufacturer-assigned product that channels and other retailers can recognize.
It matters because channels like Google Shopping use the GTIN to understand exactly what you are selling, match it to other sellers, and pull in extra context like specs and reviews. A correct GTIN often means broader reach and stronger matching; a missing or wrong one can suppress a product or get it disapproved.
In the feed it lives in the gtin attribute. Common mistakes are using your own internal SKU here, padding or truncating the digits, or failing the check-digit validation that confirms the number is real. If a product genuinely has no GTIN (custom or handmade goods), you signal that with identifier_exists instead of inventing one.
MartechFlow can map your source field to gtin, validate the format and check digit before export, and flag rows where the value is missing or malformed so you can fix them in one queue rather than discovering it from a channel rejection.