CAT_VALIDATION_ERROR_PRODUCT_ID_INVALID is raised when the product id field is empty, contains unsupported characters, or exceeds Snap's length limits. Stable, URL-safe IDs that never change between feed refreshes are required.
Snap Catalog Manager 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.