GET /api/vat/validate

Validate a VAT number against the official registry (Pro subscription required). EU member states and Northern Ireland (XI) are checked against the European Commission's VIES service, Norwegian (NO) numbers against the Brønnøysund Register Centre (data.brreg.no, NLOD licence) and Swiss (CHE) numbers against the Swiss UID register. UK (GB) validation against HMRC is coming soon: until it is enabled, GB numbers are format-checked and then answered valid: null, status: unavailable with upstream_error: SOURCE_NOT_CONFIGURED (HTTP 503, not counted against your daily quota) — see /api/vat/validate/status. Numbers are format- and checksum-checked first, so an obviously invalid number returns status: invalid_format without an upstream lookup. Results are cached (valid answers 24h, invalid 1h). If the registry is unavailable, the response is valid: null, status: unavailable (HTTP 503) — never "invalid" — or, when a previous definitive answer exists, that answer flagged stale: true (HTTP 200). The response also carries the country's standard VAT rate from the /api/vat/rates dataset. Norwegian answers include an attribution string required by the NLOD licence ("Contains data under the Norwegian licence for Open Government data (NLOD) distributed by the Brønnøysund Register Centre"); keep it when you redistribute that data. attribution is null for other countries.