Validate a European Union VAT number against the official VIES (VAT Information Exchange System) register in real time. Confirms whether the VAT identifier is currently registered for intra-EU trade and, when the member state discloses them, returns the registered business name and address. Covers the 27 EU member states (Greece as EL) plus Northern Ireland (XI); Great Britain (GB) is not in VIES. Pass either a full identifier (vat=DE811569869) or country + number. Returns {valid, countryCode, vatNumber, name, address, requestDate, reason}. When a member-state register is temporarily down, returns a retryable 503 rather than a false negative. Data from the European Commission VIES service.