A phone number in your ad text or extension is not formatted correctly for the target market - missing digits, wrong country code length, or non-standard separators.
Microsoft Merchant 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.