# BT-42 Seller contact telephone number

Telephone number for the seller contact point.

## Quick answer

Telephone number for the seller contact point.

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

## In plain language

Telephone number for the seller contact point.

Telephone number for the seller contact point.

Provide this when the buyer may need to resolve invoice questions by phone.

## What you usually enter here

Telephone number

Typical valid values include: +49 221 1234567

Optional according to EN 16931-1.

## What goes wrong often

Avoid values like:

## Examples in context

Provide this when the buyer may need to resolve invoice questions by phone.

Optional according to EN 16931-1.

## Valid Examples

- +49 221 1234567

## Related Fields

Provide this when the buyer may need to resolve invoice questions by phone.

- [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:
0..1

### Requirement:
Optional

### Max Length:
50 characters

### Since Version:
Optional

## XML Implementation

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

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

## Why the standard cares about this field

### Business Context
Provide this when the buyer may need to resolve invoice questions by phone.

### 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)