The submitted GTIN is registered to a different brand or product in GS1's database. Walmart cross-references GTINs and rejects mismatches to prevent counterfeit and incorrect listings.
GS1 assigns GTIN prefixes to specific brand owners. If your brand value doesn't match the registered GS1 brand for that GTIN, ingestion fails. This also fires when sellers reuse a third-party GTIN, use recycled UPCs from a UPC reseller, or submit private-label products with another company's barcodes.