# BT-155 Invoice line item seller's identifier

Identifier assigned by the seller for the invoiced item (for example SKU or article number).

## Quick answer

Identifier assigned by the seller for the invoiced item (for example SKU or article number).

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

- validate
- convert

## In plain language

Identifier assigned by the seller for the invoiced item (for example SKU or article number).

Identifier assigned by the seller for the invoiced item (for example SKU or article number).

Supports seller catalog and article reference mapping (BT-155).

## What you usually enter here

Alphanumeric item identifier

Typical valid values include: SKU123456, PROD-ABC-001, 1.1.30

Optional according to EN 16931.

## What goes wrong often

Avoid values like: , AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Relevant rule codes: BR-2

## Examples in context

Supports seller catalog and article reference mapping (BT-155).

Optional according to EN 16931.

## Valid Examples

- SKU123456
- PROD-ABC-001
- 1.1.30

## Invalid Examples

- AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

## Related Fields

Supports seller catalog and article reference mapping (BT-155).

- [BT-153 Invoice line item name](/resources/xrechnung/bt-153-invoice-line-item-name)
- [BT-154 Invoice line item description](/resources/xrechnung/bt-154-invoice-line-item-description)
- [BT-142 Invoice line item standard identifier](/resources/xrechnung/bt-142-invoice-line-item-standard-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-155

### Data Type:
identifier

### Cardinality:
0..1

### Requirement:
Optional

### Max Length:
50 characters

### Since Version:
Optional

## XML Implementation

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

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

## Validation Rules

### BR-2
BR-2

## Why the standard cares about this field

### Business Context
Supports seller catalog and article reference mapping (BT-155).

### Legal Requirement
Optional according to EN 16931.

## 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)