# BT-126 Invoice line identifier

A unique identifier for the individual line item within the invoice.

> BT-126 (Invoice line identifier) is the per-line index used to reference each invoice line uniquely within the document. Mandatory under EN 16931. Typically a sequential integer ("1", "2", "3"); reused across allowance/charge references. Must be unique within the invoice. Example: 1.
>
> BT-126 · EN 16931 / XRechnung 3.x

## BT Reference Card

Key EN 16931 and XRechnung facts for this business term.

- **BT code**: BT-126
- **Name**: Invoice line identifier
- **Cardinality**: Mandatory (M)
- **Business group**: BG-25 INVOICE LINE
- **Data type**: Identifier
- **Example value**: 1

## Quick answer

A unique identifier for the individual line item within the invoice.

> **Line items**: The goods or services on each invoice line, including quantities, prices, and VAT.

- [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-126)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-126)

## In plain language

A unique identifier for the individual line item within the invoice.

A unique identifier for the individual line item within the invoice.

Essential for referencing and processing individual line items in automated systems.

## What you usually enter here

Unique identifier within the invoice, mirroring the original position number

Typical valid values include: 1, 2, 10, 001

Mandatory for each invoice line according to EN 16931-1.

## What goes wrong often

Avoid values like: , 0, -1

Relevant rule codes: BR-21

## Examples in context

Essential for referencing and processing individual line items in automated systems.

Mandatory for each invoice line according to EN 16931-1.

## Valid Examples

- 1
- 2
- 10
- 001
- 1.1.30
- 2.1.40
- LINE-001

## Invalid Examples

- 0
- -1

## Related Fields

Essential for referencing and processing individual line items in automated systems.

- [BT-127 Invoice line note](/resources/xrechnung/bt-127-invoice-line-note)
- [BT-128 Invoice line object identifier](/resources/xrechnung/bt-128-invoice-line-object-identifier)
- [BT-129 Invoice line quantity](/resources/xrechnung/bt-129-invoice-line-quantity)
- [BT-130 Invoice line quantity unit of measure code](/resources/xrechnung/bt-130-invoice-line-quantity-unit-of-measure-code)
- [BT-131 Invoice line net amount](/resources/xrechnung/bt-131-invoice-line-net-amount)
- [BT-132 Referenced purchase order line identifier](/resources/xrechnung/bt-132-referenced-purchase-order-line-identifier)

## 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-126

### Data Type:
identifier

### Cardinality:
1..1

### Requirement:
Mandatory

### Since Version:
XRechnung 1.0+

## XML Implementation

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

### CII (UN/CEFACT) Syntax
```
/CrossIndustryInvoice/SupplyChainTradeTransaction/ApplicableHeaderTradeSettlement/ram:SpecifiedTradeSettlementLineMonetarySummation/ram:LineID
```

## Validation Rules

### BR-21
BR-21

## Check whether your XRechnung sets BT-126 correctly

Upload the XML file to the free validator. It applies the KoSIT rules for XRechnung 3.0 and names each finding with its rule ID, for this field for example BR-21. Creating a new invoice instead? The converter checks the invoice against the same rules and shows the findings before download.

- [Validate XML](/en/xrechnung-validator)
- [Convert invoice](/en/pdf-to-xrechnung)

Free, no account needed. XML file up to 2 MB.

## Why the standard cares about this field

### Business Context
Essential for referencing and processing individual line items in automated systems.

### Legal Requirement
Mandatory for each invoice line according to EN 16931-1.

## Official sources and tools

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