UBL-SR-07: A preceding invoice reference needs the invoice number

What it means

When an invoice or credit note refers to an earlier invoice (BG-3), that reference must contain the number of the earlier invoice (BT-25). The rule checks every cac:BillingReference for a cbc:ID inside its cac:InvoiceDocumentReference. A reference with no cbc:ID element fails, even if it holds the date of the earlier invoice (BT-26), which is optional.

Why it matters

EN 16931 requires an earlier invoice number in every preceding invoice reference.

How to fix it

In your invoicing software, find the field that links a credit note or corrected invoice to the original, often called original invoice or reference invoice. Enter the number exactly as it is printed on the original. If no earlier invoice is involved, clear the link so the software leaves the reference out. In the XML, the number is cbc:ID in cac:BillingReference/cac:InvoiceDocumentReference.

The rule as published

If there is a preceding invoice reference, the preceding invoice number shall be present

Where this rule applies