BR-09
A rule of the European standard EN 16931 – applies to every invoice following the standard, including Peppol BIS Billing 3.0.
What this error means
BR-09
The seller's postal address has no country code (BT-40).
How to fix it
In the seller address add cac:Country → cbc:IdentificationCode with a two-letter code, e.g. LT or PL.