The Product Identifier Type (UPC, GTIN, EAN, ISBN) or its value is missing or doesn't match the declared 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.