antubis

This plugin extends WooCommerce and Booster for WooCommerce. It adds a new key “vat_number” to billing address when requested by API call. Also it will auto fill the VAT value when creating a manual order.
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WooCommerce VAT to API

Show VAT number as part of billing address in the WooCommerce API

marekma

The plugin allow you to validate your clients VAT Number using the online VIES service from Agenzia delle Entrate.
If you don’t currently have a VAT Number field you can easily add one from the settings menu. If you already have one just specify the field ID and the validation will take place on your existing field.
For more information about VIES see <a href="https://telematici.agenziaentrate.gov.it/VerificaPIVA/Scegli.jsp" rel="nofollow ugc">https://telematici.agenziaentrate.gov.it/VerificaPIVA/Scegli.jsp</a>
Based on <a href="https://github.com/pH-7/eu-vat-validator" rel="nofollow ugc">eu-vat-validator</a>: a simple and clean PHP library that validates EU VAT registration numbers against the central ec.europa.eu database.

VIES Validator

Add a VAT Number (Partita IVA) field to Woocommerce checkout and validate it using the VIES API service from Agenzia delle Entrate.

WooCommerce VAT to API vs VIES Validator