BR-52: Supporting document without reference (BT-122)

StandardEN 16931-1 (European e-invoicing semantic model)SeverityError: the invoice is rejectedSyntaxUBL, CIIBusiness terms

BG-24 Additional supporting documents
BT-122 Supporting document reference

Applies toEvery EN 16931 invoice: XRechnung, ZUGFeRD 2.x / Factur-X (profiles EN 16931, EXTENDED, XRECHNUNG), Peppol BIS Billing 3.0, and national CIUS such as the Dutch NLCIUS or the Italian/Spanish profiles.

Official rule text

[BR-52] Each Additional supporting document (BG-24) shall contain a Supporting document reference (BT-122).

Why this error occurs

Each additional supporting document (BG-24) must carry an identifier: cbc:ID in cac:AdditionalDocumentReference (UBL) or ram:IssuerAssignedID in ram:AdditionalReferencedDocument (CII). Without a reference the receiver cannot tell attachments apart or match them to time sheets, delivery notes or contracts. The error appears when software attaches a PDF but leaves the ID empty, or when the file name is written into cbc:DocumentDescription instead of cbc:ID.

How to fix it

In UBL give every cac:AdditionalDocumentReference a non-empty cbc:ID (first child), e.g. the delivery note number or the file name of the attachment; cbc:DocumentDescription (BT-123) and cac:Attachment are optional additions. In CII set ram:IssuerAssignedID as the first child of each ram:AdditionalReferencedDocument, with ram:TypeCode 916 for supporting documents. Note that in UBL the invoiced object identifier (BT-18, DocumentTypeCode 130) uses the same element and also needs cbc:ID.

Example (valid)

<cac:AdditionalDocumentReference>
  <cbc:ID>LS-2026-0455</cbc:ID>
  <cbc:DocumentDescription>Delivery note</cbc:DocumentDescription>
  <cac:Attachment><cbc:EmbeddedDocumentBinaryObject mimeCode="application/pdf" filename="LS-2026-0455.pdf">JVBERi0...</cbc:EmbeddedDocumentBinaryObject></cac:Attachment>
</cac:AdditionalDocumentReference>

What the validator checks

Checked element (context):

UBL

cac:AdditionalDocumentReference

Test (XPath):

normalize-space(cbc:ID) != ''

CII

//ram:AdditionalReferencedDocument

Test (XPath):

normalize-space(ram:IssuerAssignedID) != ''

Check your invoice

Drop your XML or PDF on the validator and every failed rule is linked to its page here. Free, no account, the file is not stored.

Check your invoice →

Same check via API:

curl -F file=@invoice.xml https://einvoicechecker.com/v1/validate

Related rules

BR-01 Specification identifier (BT-24) is missing
BR-02 Invoice number (BT-1) is missing
BR-03 Invoice issue date (BT-2) is missing
BR-04 Invoice type code (BT-3) is missing
BR-05 Invoice currency code (BT-5) is missing
BR-06 Seller name (BT-27) is missing
BR-07 Buyer name (BT-44) is missing
BR-08 Seller postal address is missing

Frequently asked questions

What does BR-52 mean?

BR-52 is a en 16931 core rule: Each Additional supporting document (BG-24) shall contain a Supporting document reference (BT-122).

Will my invoice be rejected because of BR-52?

Yes. BR-52 is flagged "fatal"; validators (KoSIT, Peppol access points, the German ZRE/OZG-RE portals) reject the invoice until it is fixed.

Which formats does BR-52 apply to?

Every EN 16931 invoice: XRechnung, ZUGFeRD 2.x / Factur-X (profiles EN 16931, EXTENDED, XRECHNUNG), Peppol BIS Billing 3.0, and national CIUS such as the Dutch NLCIUS or the Italian/Spanish profiles. Syntax: UBL and CII.

Source: EN 16931-1:2017 schematron (CEN TC434, via Peppol BIS 3.0.20). Catalogue generated from the official schematron on 2026-10-14.