CIUS-FR — SIRET missing or failing the Luhn check

Since 2026-09-01 every French VAT-registered business must be able to receive structured e-invoices, and the CIUS-FR overlay requires a valid SIRET for both parties.

• Blocks a missing or wrong-length SIRET and a SIRET that fails the Luhn check digit.
• Applies the La Poste SIREN 356000000 exception instead of flagging a false positive.
• For a non-French buyer, requires its VAT identifier and validates the national format.