The VIES (VAT Information Exchange System) is a service of the European Commission with which you can check if a business is registered/allowed to trade cross-border within the European Union.
While appearing to be a database, the VIES is rather comparable to a search engine and it is available in 23 languages. Naturally, there are two possible outcomes: the information searched for can be found in the national database where the business should be located.. or not. Consequently, the EU VAT information is valid or invalid. As there are some countries within the EU which require a separate registration for intra-EU transactions, an invalid number could be the consequence of a not finished registration. In most cases, when the number is invalid, the VAT number simply doesn’t exist or has not been activated.