# BT-122 Supporting Document Reference

An identifier for a supporting document referenced from the invoice.

## Quick answer

An identifier for a supporting document referenced from the invoice.

> **Taxes and totals**: VAT treatment, tax breakdowns, and document totals that validators check closely.

- validate
- convert

## In plain language

An identifier for a supporting document referenced from the invoice.

An identifier for a supporting document referenced from the invoice.

Links the invoice to evidence such as contracts, delivery notes, timesheets, or other attachments.

## What you usually enter here

Document identifier

Typical valid values include: DELIVERY-NOTE-1001, CONTRACT-2025-07, TIMESHEET-42

Each supporting document group must contain a supporting document reference according to BR-52.

## What goes wrong often

Avoid values like: ,

Relevant rule codes: BR-52

## Examples in context

Links the invoice to evidence such as contracts, delivery notes, timesheets, or other attachments.

Each supporting document group must contain a supporting document reference according to BR-52.

## Valid Examples

- DELIVERY-NOTE-1001
- CONTRACT-2025-07
- TIMESHEET-42

## Related Fields

Links the invoice to evidence such as contracts, delivery notes, timesheets, or other attachments.

- [BT-123 Supporting Document Description](/resources/xrechnung/bt-123-supporting-document-description)
- [BT-124 External Document Location](/resources/xrechnung/bt-124-external-document-location)
- [BT-125 Attached Document](/resources/xrechnung/bt-125-attached-document)

## XML mapping and field facts

Open the technical reference if you need XML paths, validator rule codes, legal wording, or schema-specific mapping details.

### Field ID:
BT-122

### Data Type:
identifier

### Cardinality:
1..1

### Requirement:
Mandatory

### Since Version:
Mandatory when BG-24 supporting document is provided

## XML Implementation

### UBL 2.1 Syntax
```
/Invoice/cac:AdditionalDocumentReference/cbc:ID
```

### CII (UN/CEFACT) Syntax
```
/CrossIndustryInvoice/SupplyChainTradeTransaction/ApplicableHeaderTradeAgreement/ram:AdditionalReferencedDocument/ram:IssuerAssignedID
```

## Validation Rules

### BR-52
BR-52

## Why the standard cares about this field

### Business Context
Links the invoice to evidence such as contracts, delivery notes, timesheets, or other attachments.

### Legal Requirement
Each supporting document group must contain a supporting document reference according to BR-52.

## Official sources and tools

- [KoSIT Validator](https://erechnungsvalidator.service-bw.de/)
- [Invoice Converter](/pdf-to-xrechnung)
- [XRechnung Standard](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)