BR-CO-09: VAT identifier missing country prefix
Severity: error
What it means
The Seller VAT identifier (BT-31), Seller tax representative VAT identifier (BT-63), or Buyer VAT identifier (BT-48) does not start with a valid ISO 3166-1 alpha-2 country prefix (Greece may use 'EL').
Most common cause
The two-letter country code was stripped from the VAT identifier, e.g. 'DE123456789' became '123456789'.
How to fix it
Restore the ISO country prefix on the VAT identifier at the source. Not auto-repaired: this touches a party identity (CLAUDE.md invariant).