# UBL-SR-16

> Buyer identifier shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-16

## Official rule text

Buyer identifier shall occur maximum once

## Why did my invoice fail UBL-SR-16?

The Buyer identifier (BT-46), which is the electronic identifier of the buyer under cac:AccountingCustomerParty/cac:Party/cac:PartyIdentification/cbc:ID, may be stated at most once on an invoice. EN 16931 models BT-46 as a single 0..1 term, so a buyer can only be given one such identifier.

## Common causes

- A mapping loop emits cbc:ID for every buyer identifier stored in the source system (e.g. an internal customer number and a GLN).
- Both a scheme-qualified and an unqualified PartyIdentification/ID are written for the same buyer.
- Merging two data sources duplicates the buyer identification element.

## How do I fix it?

```
Keep a single identifier: <cac:PartyIdentification><cbc:ID schemeID="0088">7300010000001</cbc:ID></cac:PartyIdentification> and remove any additional cac:PartyIdentification blocks under AccountingCustomerParty/Party.
```