Category-specific required attributes (color, material, size, etc.) are not populated. Walmart enforces these per product type spec.
Walmart Seller Center's product schema has format and value rules per attribute. This issue is typically: missing a required attribute for the category, an invalid enum value (e.g., 'XL' submitted where 'M, L, XL' is the valid set), out-of-range numbers, or attributes that conflict across the feed.