The submitted GTIN is structurally valid but belongs to a different product, often because a code was reused across SKUs.
Product identifiers (GTIN, MPN, brand) anchor Google's matching of your product to its catalog. Issues here typically come from non-numeric characters in GTIN, mismatched UPC vs EAN length, brand-GTIN ownership conflicts in GS1's database, or duplicate GTINs across multiple SKUs.