# UBL-SR-09

> Seller name shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-09

## Official rule text

Seller name shall occur maximum once

## Why did my invoice fail UBL-SR-09?

The Seller name (BT-27), the full official name under which the seller is registered, may occur at most once. In UBL this is cac:AccountingSupplierParty/cac:Party/cac:PartyLegalEntity/cbc:RegistrationName, which must be single-valued.

## Common causes

- Both cac:PartyName and cac:PartyLegalEntity are mapped and the validator sees two seller-name sources.
- Multiple cac:PartyLegalEntity elements are emitted for one seller.
- Registration name is duplicated across trading and legal name mappings.

## How do I fix it?

```
Keep one legal registration name: <cac:PartyLegalEntity><cbc:RegistrationName>ACME Trading Ltd</cbc:RegistrationName></cac:PartyLegalEntity> and remove duplicate seller-name elements.
```