CAT_VALIDATION_ERROR_SIZE_INVALID fires when size is empty, exceeds Snap's character cap, or contains unsupported characters. Use compact size labels (S, 32, 12oz) and rely on size_type and size_system for granularity.
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.