BR-AE-10
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-AE-10
The VAT breakdown with reverse charge (AE) has no reason — the text "Reverse charge" (BT-120) or the code (BT-121) is required.
How to fix it
Add cac:TaxSubtotal → cac:TaxCategory → cbc:TaxExemptionReason with the text "Reverse charge".