wc_field_blur_update_checkout.php

<?php
/*
   update checkout on billing postcode field blur
*/

function wc_field_blur_update_checkout(){?>
            
            <script>
            jQuery("#billing_postcode").blur(function(){      
                jQuery( 'body' ).trigger( 'update_checkout' );
            });
            </script>   
            <?php
            }            
            add_action("wp_footer","wc_field_blur_update_checkout");