Manipulate VAT field position on Invoicing with InoiceXpress for WooCommerce

woocommerce_checkout_fields.php

<?php
add_filter( 'woocommerce_checkout_fields', 'my_woocommerce_checkout_fields', 60 );
function my_woocommerce_checkout_fields( $fields ) {
	if ( isset( $fields['billing']['billing_VAT_code'] ) ) {
		$fields['billing']['billing_VAT_code']['class']    = array( 'form-row-first' ); //Or form-row-last
		$fields['billing']['billing_VAT_code']['clear']    = true; //Or false if we use form-row-last
		$fields['billing']['billing_VAT_code']['priority'] = 120; //120 is the default position, change this to move it up or down on the form
	}
	return $fields;
}