# 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

Canonical EN 16931 / XRechnung facts for this business term — citable from this anchor.

- **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.

## 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-2

## 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-2
BR-2

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