# UBL-SR-53

> CompanyID (VAT Identifier) must be stated when providing the PartyTaxScheme/TaxScheme/ID.

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-sr-53

## Official rule text

CompanyID (VAT Identifier) must be stated when providing the PartyTaxScheme/TaxScheme/ID.

## Why did my invoice fail UBL-SR-53?

When a party (Seller BG-4 or Buyer BG-7) declares a tax registration via cac:PartyTaxScheme with a TaxScheme/ID (typically 'VAT'), the party's VAT identifier (BT-31 Seller VAT / BT-48 Buyer VAT) must be supplied as cac:PartyTaxScheme/cbc:CompanyID. A TaxScheme entry without a CompanyID would assert a tax registration with no actual identifier.

## Common causes

- cac:PartyTaxScheme includes a cac:TaxScheme/cbc:ID but omits cbc:CompanyID.
- The VAT number was placed under PartyLegalEntity/CompanyID (BT-30 legal registration) instead of PartyTaxScheme/CompanyID.
- An empty CompanyID element was emitted for a party that has no VAT number (the whole PartyTaxScheme should then be removed).

## How do I fix it?

```
Provide the identifier: <cac:PartyTaxScheme><cbc:CompanyID>SI12345678</cbc:CompanyID><cac:TaxScheme><cbc:ID>VAT</cbc:ID></cac:TaxScheme></cac:PartyTaxScheme>.
```