FORMAT-NON-PEPPOL-CIUS
A structural check before the rule layers – the file must first be readable as a valid XML document.
What this error means
FORMAT-NON-PEPPOL-CIUS
The invoice is UBL, but declares a national profile (e.g. XRechnung) instead of Peppol BIS Billing 3.0. National rules are not checked yet.
How to fix it
If the invoice is meant for the Peppol network, set CustomizationID to urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0.