Portuguese VAT number (NIF)
In Portugal the VAT number is the NIF: nine digits, the last being a check digit. Between EU businesses it takes the prefix PT. In VIES you choose Portugal and type the digits with no spaces or dots.
An individual's NIF is personal data: Decree-Law 14/2013, article 4, sets the structure for individuals, with a first digit from 1 to 4. A number can have a correct check digit and still not be registered for intra-EU trade: VIES is what answers that.
From the team behind this site: Portuguese invoices for online stores, with InvoiceXpress. See Caravel Invoice PT