Streamline Your WooCommerce Store with Automatic EU VAT Validation

functions.php

<?php
add_action( 'woocommerce_checkout_process', 'automatic_validation_eu_vat' );
function automatic_validation_eu_vat() {
   $vat = str_replace( array( ' ', '.', '-', ',', ',' ), '', wc_clean( $_POST['billing_vat'] ) );
   if ( ! empty( $vat ) ) {
       $response = wp_remote_get( "http://ec.europa.eu/taxation_customs/vies/vatResponse.html?ms=" . substr( $vat, 0, 2 ) . "&iso=" . substr( $vat, 2 ) );
       
       if ( is_wp_error( $response ) ) {
           wc_add_notice( 'There was a problem connecting to the VAT validation service. Please try again later.', 'error' );
       } else {
           // Retrieve the body and parse the JSON response
           $body   = wp_remote_retrieve_body( $response );
           $result = json_decode( $body, true );

           // Check if the VAT number is valid
           if ( $result['isValid'] !== true ) {
               wc_add_notice( 'Please enter a valid VAT number.', 'error' );
           }
       }
   }
}