[WordPress] WooCommerce 訂單取消或失敗發信通知客戶

woocommerce_email_recipient_cancelled_failed_order_email.php

<?php
//https://stackoverflow.com/questions/51635878/send-cancelled-and-failed-order-email-to-customer-in-woocommerce-3
add_filter( 'woocommerce_email_recipient_cancelled_order', 'wc_cancelled_order_add_customer_email', 10, 2 );
add_filter( 'woocommerce_email_recipient_failed_order', 'wc_cancelled_order_add_customer_email', 10, 2 );
function wc_cancelled_order_add_customer_email( $recipient, $order ){
    // Avoiding errors in backend (mandatory when using $order argument)
    if ( ! is_a( $order, 'WC_Order' ) ) return $recipient;

    return $recipient .= "," . $order->get_billing_email();
}