Send email on custom order status change in WooCommerce

To send an email notification when a custom order status changes in WooCommerce, you can use the woocommerce_order_status_{status} action hook. 

WooCommerce: Sending an email notification when custom order status change

Just copy and paste below code into your child theme’s functions.php file.

// Adding action for 'order shipped'
add_filter( 'woocommerce_email_actions', 'custom_email_actions', 20, 1 );
function custom_email_actions( $action ) {
    $actions[] = 'woocommerce_order_status_wc-order-shipped';
    return $actions;
}

add_action( 'woocommerce_order_status_wc-order-shipped', array( WC(), 'send_transactional_email' ), 10, 1 );

// Sending an email notification when order get 'order-shipped' status
add_action('woocommerce_order_status_order-shipped', 'backorder_status_custom_notification', 20, 2);
function backorder_status_custom_notification( $order_id, $order ) {
    // HERE below your settings
    $heading   = __('Your order has been shipped','woocommerce');
    $subject   = '[{site_title}] shipped order ({order_number}) - {order_date}';

    // Getting all WC_emails objects
    $mailer = WC()->mailer()->get_emails();

    // Customizing Heading and subject In the WC_email processing Order object
    $mailer['WC_Email_Customer_Processing_Order']->heading = $heading;
    $mailer['WC_Email_Customer_Processing_Order']->settings['heading'] = $heading;
    $mailer['WC_Email_Customer_Processing_Order']->subject = $subject;
     $mailer['WC_Email_Customer_Processing_Order']->settings['subject'] = $subject;

    // Sending the customized email
    $mailer['WC_Email_Customer_Processing_Order']->trigger( $order_id );
}

Conclusion

Thanks for reading 🙏, I hope you will get this code snippet helpful for your project.