# UBL-SR-28

> Mandate reference identifier shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-28

## Official rule text

Mandate reference identifier shall occur maximum once

## Why did my invoice fail UBL-SR-28?

The Mandate reference identifier (BT-89), in cac:PaymentMeans/cac:PaymentMandate/cbc:ID, is the unique SEPA direct-debit mandate reference agreed between seller and buyer, and it may occur at most once. A single direct-debit mandate applies per invoice, so only one mandate reference is allowed.

## Common causes

- More than one cac:PaymentMandate is emitted, each with its own ID.
- The mandate ID is repeated within a single PaymentMandate element.
- A mandate reference is added even though the payment means is not direct debit, colliding with another mapping.

## How do I fix it?

```
Provide one mandate reference: <cac:PaymentMeans>...<cac:PaymentMandate><cbc:ID>MNDT-2026-000123</cbc:ID></cac:PaymentMandate></cac:PaymentMeans> and remove duplicate PaymentMandate/ID entries.
```