# BT-42 Seller contact telephone number

Telephone number for the seller contact point.

## Quick answer

> **Seller details**: Who issued the invoice and how the recipient can identify that business reliably.

- [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-42)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-42)

## In plain language

This number lets the buyer resolve invoice questions with the seller contact.

## What you usually enter here

Telephone number

Typical valid values include: +49 221 1234567

Optional in base EN 16931. XRechnung requires seller contact group BG-6 through BR-DE-2 and requires BT-42 through BR-DE-6.

## Where the field sits

BT-42 belongs to the Seller part of the invoice. UBL 2.1 Syntax: Invoice › cac:AccountingSupplierParty › cac:Party › cac:Contact › cbc:Telephone. CII (UN/CEFACT) Syntax: rsm:CrossIndustryInvoice › rsm:SupplyChainTradeTransaction › ram:ApplicableHeaderTradeAgreement › ram:SellerTradeParty › ram:DefinedTradeContact › ram:TelephoneUniversalCommunication › ram:CompleteNumber.

## What goes wrong often

Relevant rule codes: BR-DE-2, BR-DE-6

## Valid Examples

- +49 221 1234567

## Related Fields

- [BT-41 Seller contact point](/resources/xrechnung/bt-41-seller-contact-point)
- [BT-43 Seller contact email address](/resources/xrechnung/bt-43-seller-contact-email-address)

## 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-42

### Data Type:
text

### Cardinality:
1..1

### Requirement:
Mandatory

### Max Length:
50 characters

### Since Version:
XRechnung 1.0+

## XML Implementation

### UBL 2.1 Syntax
```
/Invoice/cac:AccountingSupplierParty/cac:Party/cac:Contact/cbc:Telephone
```

### CII (UN/CEFACT) Syntax
```
/rsm:CrossIndustryInvoice/rsm:SupplyChainTradeTransaction/ram:ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:DefinedTradeContact/ram:TelephoneUniversalCommunication/ram:CompleteNumber
```

## Validation Rules

### BR-DE-2
BR-DE-2

### BR-DE-6
BR-DE-6

## Check whether your XRechnung sets BT-42 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-DE-2, BR-DE-6. 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.

## 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)