BR-S-01
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-S-01
There is a line or an allowance / charge with standard-rated VAT (category S), but the seller has no VAT identifier (BT-31).
How to fix it
Provide the seller's VAT number: cac:AccountingSupplierParty → cac:PartyTaxScheme → cbc:CompanyID with TaxScheme VAT.