DEFINITION
A VAT number identifies a business registered for VAT. In the EU it is written as a two-letter country prefix followed by the national number: DE123456789, FR12345678901, NL123456789B01. Greece uses EL, and Northern Ireland uses XI for trade in goods.
For trade between EU countries, the buyer's VAT number is not a formality. Since 1 January 2020, a valid VAT number of the customer, registered for intra-EU trade, is a condition of the 0% rate on an intra-community supply. A number can be valid at home but not activated for intra-EU trade, or be cancelled later, so it has to be checked against VIES, the EU's register, and the check kept as proof.
The number also has to appear on the invoice, next to the seller's own, and in the seller's EC Sales List.
HOW KOLIBRA HELPS
Kolibra checks a partner's VAT number against VIES when you add them, and again on every deal, filing a timestamped proof on the deal. You can also check any number for free with the VAT number check.