# BT-57 Buyer contact telephone number

Telephone number for the buyer contact point.

## Quick answer

> **Buyer details**: Who receives the invoice and which buyer records or routing data must match.

- [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-57)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-57)

## In plain language

Provide this only when the invoice recipient expects telephone contact details in the structured invoice.

## What you usually enter here

Telephone number

Typical valid values include: +49 30 123456

Optional according to EN 16931-1.

## Where the field sits

BT-57 belongs to the Buyer part of the invoice. UBL 2.1 Syntax: Invoice › cac:AccountingCustomerParty › cac:Party › cac:Contact › cbc:Telephone. CII (UN/CEFACT) Syntax: rsm:CrossIndustryInvoice › rsm:SupplyChainTradeTransaction › ram:ApplicableHeaderTradeAgreement › ram:BuyerTradeParty › ram:DefinedTradeContact › ram:TelephoneUniversalCommunication › ram:CompleteNumber.

## Valid Examples

- +49 30 123456

## Related Fields

- [BT-56 Buyer contact point](/resources/xrechnung/bt-56-buyer-contact-point)
- [BT-58 Buyer contact email address](/resources/xrechnung/bt-58-buyer-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-57

### Data Type:
text

### Cardinality:
0..1

### Requirement:
Optional

### Max Length:
50 characters

## XML Implementation

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

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

## 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)