# BT-128 Invoice line object identifier

An identifier for an object on which the invoice line is based, such as an order line, despatch advice line, or tender line.

## Quick answer

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

- [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-128)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-128)

## In plain language

Links the invoice line to the corresponding line in the source document (order, tender, etc.).

## What you usually enter here

Alphanumeric identifier with meaningful reference

Typical valid values include: PO-001-1, ORDER-123-5, TENDER-ABC-2

Optional but recommended for traceability and audit purposes.

## Where the field sits

BT-128 belongs to the Lines part of the invoice. UBL 2.1 Syntax: Invoice › cac:InvoiceLine › cac:DocumentReference › cbc:ID. CII (UN/CEFACT) Syntax: rsm:CrossIndustryInvoice › rsm:SupplyChainTradeTransaction › ram:IncludedSupplyChainTradeLineItem › ram:SpecifiedLineTradeSettlement › ram:AdditionalReferencedDocument › ram:IssuerAssignedID.

## What goes wrong often

Avoid values like: reference

## Valid Examples

- PO-001-1
- ORDER-123-5
- TENDER-ABC-2

## Invalid Examples

- reference

## Related Fields

- [BT-126 Invoice line identifier](/resources/xrechnung/bt-126-invoice-line-identifier)
- [BT-13 Purchase Order Reference](/resources/xrechnung/bt-13-purchase-order-reference)

## 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-128

### Data Type:
identifier

### Cardinality:
0..1

### Requirement:
Optional

### Max Length:
50 characters

## XML Implementation

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

### CII (UN/CEFACT) Syntax
```
/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:IncludedSupplyChainTradeLineItem/ram:SpecifiedLineTradeSettlement/ram:AdditionalReferencedDocument/ram:IssuerAssignedID
```

## Create an XRechnung from your PDF

The converter reads the invoice and shows the fields it found before download, so you can check and correct the values. No PDF? Fill in the XRechnung directly in the form.

- [Convert invoice](/en/pdf-to-xrechnung)
- [Fill in XRechnung in the form](/en/create-xrechnung)

Trying it and buying a single conversion work without an account. Subscriptions from €10/month with annual billing (excl. taxes), or €5 per conversion (excl. taxes) without a subscription.

## 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)