Availability is set to 'in stock' but the landing page shows the item is unavailable, which causes Shopping Ads disapproval.
Pinterest Catalogs'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.