# BT-31 Seller VAT Identifier The seller's VAT identifier (also known as VAT registration number). For German companies, this follows the format DE + 9 digits. > BT-31 is the seller's VAT identifier. It is conditional. Select BT-31, BT-32, or BT-63 according to the VAT category; category O forbids BT-31. Example: DE123456789. > > BT-31 ยท EN 16931 / XRechnung 3.x ## BT Reference Card Key EN 16931 and XRechnung facts for this business term. - **BT code**: BT-31 - **Name**: Seller VAT Identifier - **Cardinality**: Conditional (C) - **Business group**: BG-4 SELLER - **Data type**: Identifier - **Example value**: DE123456789 - **Common error**: BR-CO-09 checks the VAT country prefix when BT-31 is present; it does not require BT-31. The VAT-category rules decide whether BT-31, BT-32, or BT-63 is needed. ## Quick answer The seller's VAT identifier (also known as VAT registration number). For German companies, this follows the format DE + 9 digits. > **Seller details**: Who issued the invoice and how the recipient can identify that business reliably. - [Validate XML](/en/xrechnung-validator?source=resource&bt=BT-31) - [Convert invoice](/en/pdf-to-xrechnung?source=resource&bt=BT-31) ## In plain language The seller's VAT identifier (also known as VAT registration number). For German companies, this follows the format DE + 9 digits. The seller's VAT identifier (also known as VAT registration number). For German companies, this follows the format DE + 9 digits. Use BT-31 when the VAT category rules require the seller VAT identifier. Depending on the category, BT-32 or BT-63 can be an alternative. Category O forbids BT-31. ## What you usually enter here Country code (2 letters) + national VAT number Typical valid values include: DE123456789, ATU12345678, FR12345678901, NL123456789B01 BT-31 is conditional. BR-CO-09 checks the country prefix when a VAT identifier is present; it does not require this field. The VAT category rules determine which seller tax identifier is needed. ## What goes wrong often Avoid values like: 123456789, DE12345678, DE1234567890, DE 123456789 Relevant rule codes: BR-CO-09, BR-DE-16, BR-S-02, BR-Z-02, BR-E-02, BR-AE-02, BR-G-02, BR-IC-02 ## Examples in context Use BT-31 when the VAT category rules require the seller VAT identifier. Depending on the category, BT-32 or BT-63 can be an alternative. Category O forbids BT-31. BT-31 is conditional. BR-CO-09 checks the country prefix when a VAT identifier is present; it does not require this field. The VAT category rules determine which seller tax identifier is needed. ## Valid Examples - DE123456789 - ATU12345678 - FR12345678901 - NL123456789B01 - IT12345678901 ## Invalid Examples - 123456789 - DE12345678 - DE1234567890 - DE 123456789 - de123456789 ## Related Fields Use BT-31 when the VAT category rules require the seller VAT identifier. Depending on the category, BT-32 or BT-63 can be an alternative. Category O forbids BT-31. - [BT-27 Seller Name](/resources/xrechnung/bt-27-seller-name) - [BT-30 Seller legal registration identifier](/resources/xrechnung/bt-30-seller-legal-registration-identifier) - [BT-32 Seller tax registration identifier](/resources/xrechnung/bt-32-seller-tax-registration-identifier) - [BT-48 Buyer VAT Identifier](/resources/xrechnung/bt-48-buyer-vat-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-31 ### Data Type: identifier ### Cardinality: 0..1 ### Requirement: Optional ### Max Length: 30 characters ### Since Version: Conditional (depends on VAT category) ## XML Implementation ### UBL 2.1 Syntax ``` /Invoice/cac:AccountingSupplierParty/cac:Party/cac:PartyTaxScheme/cbc:CompanyID ``` ### CII (UN/CEFACT) Syntax ``` /CrossIndustryInvoice/SupplyChainTradeTransaction/ApplicableHeaderTradeAgreement/ram:SellerTradeParty/ram:SpecifiedTaxRegistration/ram:ID[@schemeID="VA"] ``` ## Validation Rules ### BR-CO-09 BR-CO-09 ### BR-DE-16 BR-DE-16 ### BR-S-02 BR-S-02 ### BR-Z-02 BR-Z-02 ### BR-E-02 BR-E-02 ### BR-AE-02 BR-AE-02 ### BR-G-02 BR-G-02 ### BR-IC-02 BR-IC-02 ## Check whether your XRechnung sets BT-31 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-16, BR-CO-09. 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. ## Why the standard cares about this field ### Business Context Use BT-31 when the VAT category rules require the seller VAT identifier. Depending on the category, BT-32 or BT-63 can be an alternative. Category O forbids BT-31. ### Legal Requirement BT-31 is conditional. BR-CO-09 checks the country prefix when a VAT identifier is present; it does not require this field. The VAT category rules determine which seller tax identifier is needed. ## FAQ ### What is the format for German VAT identifiers? German VAT identifiers follow the format "DE" followed by exactly 9 digits (e.g., DE123456789). No spaces or special characters are allowed. ### Is the VAT identifier mandatory for all sellers? No. The VAT category determines the requirement. Some categories accept BT-32 or BT-63 instead, while category O forbids BT-31. ### How can I validate a VAT identifier? Use the EU VIES system (ec.europa.eu/taxation_customs/vies/) to validate VAT identifiers. Each country has specific format requirements. ### What about other EU countries VAT formats? Each EU country has its own VAT number format: ATU plus 8 digits, FR with 11 characters, NL with 12 characters, or IT with 11 digits. Use the full national VAT prefix and value. ## 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)