Ako pridať vlastný checkbox do pokladne vo WooCommerce

// Add custom checkout field: woocommerce_review_order_before_submit
add_action( 'woocommerce_review_order_before_submit', 'my_custom_checkout_field' );
function my_custom_checkout_field() {
echo '<div id="my_custom_checkout_field">';

woocommerce_form_field( 'tlacena_fa', array(
'type'  => 'checkbox',
'class' => array('woocommerce-form__input'),
'input_class' => array('woocommerce-form__input woocommerce-form__input-checkbox input-checkbox'),
'label' => __('Prajem si zaslať faktúru aj v tlačenej papierovej podobe.'),
),  WC()->checkout->get_value( 'tlacena_fa' ) );
 echo '</div>'  
;
}

// Save the custom checkout field in the order meta, when checkbox has been checked
add_action( 'woocommerce_checkout_update_order_meta', 'custom_checkout_field_update_order_meta', 10, 1 );

function custom_checkout_field_update_order_meta( $order_id ) {

if ( ! empty( $_POST['tlacena_fa'] ) )
update_post_meta( $order_id, 'tlacena_fa', $_POST['tlacena_fa'] );
}

// Display the custom field result on the order edit page (backend) when checkbox has been checked
add_action( 'woocommerce_admin_order_data_after_billing_address', 'display_custom_field_on_order_edit_pages', 10, 1 );
function display_custom_field_on_order_edit_pages( $order ){
$tlacena_fa = get_post_meta( $order->get_id(), 'tlacena_fa', true );
if( $tlacena_fa == 1 )
echo '<p><strong>Tlacena FA: </strong> <span style="color:green;">ANO</span></p>';
$tlacena_fa = get_post_meta( $order->get_id(), 'tlacena_fa', true );
if( $tlacena_fa == 0 )
echo '<p><strong>Tlacena FA: </strong> <span style="color:red;">NIE</span></p>';
}