# UBL-SR-18

> Buyer VAT identifier shall occur maximum once

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-18

## Official rule text

Buyer VAT identifier shall occur maximum once

## Why did my invoice fail UBL-SR-18?

The Buyer VAT identifier (BT-48) is expressed as a cac:PartyTaxScheme with cbc:CompanyID and a VAT tax scheme under AccountingCustomerParty/Party, and it may occur at most once. A buyer has a single VAT identifier, so more than one is invalid.

## Common causes

- Two cac:PartyTaxScheme elements with a VAT TaxScheme are emitted for the buyer.
- A VAT number is written both with and without the country prefix as separate entries.
- A non-VAT tax registration is incorrectly given the VAT scheme, producing a second VAT PartyTaxScheme.

## How do I fix it?

```
State the VAT id once: <cac:PartyTaxScheme><cbc:CompanyID>DK16356706</cbc:CompanyID><cac:TaxScheme><cbc:ID>VAT</cbc:ID></cac:TaxScheme></cac:PartyTaxScheme>. Remove any additional VAT-scheme PartyTaxScheme for the buyer.
```