CAT_VALIDATION_ERROR_INVALID_GOOGLE_PRODUCT_CATEGORY fires when google_product_category is not a valid taxonomy ID or full breadcrumb string. Snap matches its own taxonomy against Google's, so misspellings or outdated nodes are rejected.
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.