BR-CO-18
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-CO-18
The invoice has no VAT breakdown (BG-23) — at least one is required.
How to fix it
Add cac:TaxTotal → cac:TaxSubtotal with taxable amount, VAT amount and category.