CAT_VALIDATION_ERROR_MATERIAL_INVALID is raised when the material attribute is too long or contains marketing copy. Provide one or two material names per item, separated by a slash.
Snap Catalog Manager'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.