# UBL-SR-06

> Preceding invoice reference shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-06

## Official rule text

Preceding invoice reference shall occur maximum once

## Why did my invoice fail UBL-SR-06?

The Preceding invoice reference group (BG-3), which links a corrective or related invoice to the invoice it precedes, may occur at most once. In UBL this maps to cac:BillingReference/cac:InvoiceDocumentReference, and only one preceding invoice reference is permitted at header level in this profile.

## Common causes

- A credit note or correction references several earlier invoices, each emitted as its own cac:BillingReference.
- The reference is duplicated in both an original and a re-mapped form.
- Loop over prior billing documents outputs multiple InvoiceDocumentReference blocks.

## How do I fix it?

```
Keep a single reference: <cac:BillingReference><cac:InvoiceDocumentReference><cbc:ID>INV-2025-900</cbc:ID><cbc:IssueDate>2025-12-01</cbc:IssueDate></cac:InvoiceDocumentReference></cac:BillingReference> and remove the others.
```