Product ID is 13 characters long when Walmart expects 12 (UPC) or 14 (GTIN). Often caused by EAN-13 codes being submitted as UPC type.
Walmart Seller Center uses identifiers (GTIN, MPN, brand, SKU) to match catalog records. Issues come from invalid format (non-numeric in a GTIN field), brand-GTIN mismatches in GS1's database, duplicate IDs across SKUs, or missing required identifiers for the category.