fatal UBL
[GR-R-008-3]-When Supplier is Greek and the INVOICE URL Document reference exists, the External Reference URI should be present
cac:AdditionalDocumentReference[$isGreekSender and cbc:DocumentDescription = '##INVOICE|URL##']
string-length(normalize-space(cac:Attachment/cac:ExternalReference/cbc:URI))>0
Source: Peppol BIS Billing 3.0 Schematron, UBL (OpenPeppol, docs.peppol.eu validation artefacts 3.0.21).
Invoice XML (UBL 2.1 Invoice/CreditNote or UN/CEFACT CII D16B, max 5 MB):
Validate