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    BR – Core rules of EN 16931

    BR-52: supporting document without a reference (BT-122)

    ErrorEN 16931 business rule (CEN)

    Official message

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

    Source: CEN EN 16931, version 1.3.16

    What the message means

    A document attached to or linked from the invoice has no reference. Every attachment, whether a proof of service, a timesheet or a delivery note, needs a name or number under which the recipient can file it and find it again from the invoice. Without that reference the attachment is a nameless block for automated processing, and the invoice counts as faulty.

    Common causes

    • The software attaches the PDF but leaves the ID field of the document reference empty.
    • The reference was set only as a file name in the filename attribute, not as the ID.
    • A reference was created but the document was never added, and the block stayed empty.

    How to fix it

    Fill the ID element of every AdditionalDocumentReference with a meaningful reference, such as the number of the proof of service. The file name alone does not replace it.

    Before – invalid
    <cac:AdditionalDocumentReference>
  <cbc:ID></cbc:ID>
  <cac:Attachment>
    <cbc:EmbeddedDocumentBinaryObject mimeCode="application/pdf" filename="proof-of-service.pdf">JVBERi0xLjQK</cbc:EmbeddedDocumentBinaryObject>
  </cac:Attachment>
</cac:AdditionalDocumentReference>
    After – corrected
    <cac:AdditionalDocumentReference>
  <cbc:ID>POS-2026-0142</cbc:ID>
  <cac:Attachment>
    <cbc:EmbeddedDocumentBinaryObject mimeCode="application/pdf" filename="proof-of-service.pdf">JVBERi0xLjQK</cbc:EmbeddedDocumentBinaryObject>
  </cac:Attachment>
</cac:AdditionalDocumentReference>

    Frequently asked

    Does every attachment need its own reference?

    Yes. BT-122 is mandatory per attachment. XRechnung adds BR-DE-22: „Das "filename"-Attribut aller "EmbeddedDocumentBinaryObject"-Elemente muss eindeutig sein“ (the file names must be unique).

    Can I give a link instead of an attachment?

    Yes. An external reference (BT-124) is allowed; the document reference still needs an identifier in BT-122.

    Fields concerned

    • BG-24
    • BT-122

    Related rules

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    Technical details
    UBL · Context (XPath)
    cac:AdditionalDocumentReference
    UBL · Schematron test
    normalize-space(cbc:ID) != ''
    CII · Context (XPath)
    //ram:AdditionalReferencedDocument
    CII · Schematron test
    normalize-space(ram:IssuerAssignedID) != ''

    Explanation written on 14 September 2026