# BT-141 Invoice line item buyer's identifier

An identifier assigned by the buyer to identify the item.

## Quick answer

An identifier assigned by the buyer to identify the item.

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

## In plain language

An identifier assigned by the buyer to identify the item.

An identifier assigned by the buyer to identify the item.

Used for buyer's internal catalog and procurement systems.

## What you usually enter here

Alphanumeric product identifier

Typical valid values include: BUYER-123, CLIENT-PROD-456, INTERNAL-789

Optional according to EN 16931-1.

## What goes wrong often

Avoid values like: , AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Relevant rule codes: BR-2

## Examples in context

Used for buyer's internal catalog and procurement systems.

Optional according to EN 16931-1.

## Valid Examples

- BUYER-123
- CLIENT-PROD-456
- INTERNAL-789

## Invalid Examples

- AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

## Related Fields

Used for buyer's internal catalog and procurement systems.

- [BT-138 Invoice line item name](/resources/xrechnung/bt-138-invoice-line-item-name)
- [BT-139 Invoice line item description](/resources/xrechnung/bt-139-invoice-line-item-description)
- [BT-140 Invoice line item seller's identifier](/resources/xrechnung/bt-140-invoice-line-item-sellers-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-141

### 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:BuyersItemIdentification/cbc:ID
```

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

## Validation Rules

### BR-2
BR-2

## Why the standard cares about this field

### Business Context
Used for buyer's internal catalog and procurement systems.

### Legal Requirement
Optional 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)