[WooCommerce] Make the EU-VAT field required during checkout (and add asterisk)

wc-make-vat-required.php

add_action('woocommerce_checkout_process', 'wc_force_vat_field_to_be_not_empty');

function wc_force_vat_field_to_be_not_empty() {
    // Check if set, if its not set add an error.
    if ( ! $_POST['vat_number']);
        wc_add_notice( __( 'Please enter your VAT number.' ), 'error' );
}

// adding the asterisk (css)

body.woocommerce-checkout .address-field.vat-number label:after {
  content: " *";
  color: red;
}