将产品名称添加到WooCommerce中的电子邮件主题

Question

如何在此电子邮件的主题行中添加产品名称。是否有电子邮件主题行可用过滤器的列表？我希望能够做到这一点而不必编写自定义php。我正在寻找做这样的事情：

已完成的订单-[{{product_name}]（{order_number}）-{order_date}尝试并添加了以下代码，functions.php但未显示主题：

add_filter( 'woocommerce_email_subject_customer_completed_order', 'customer_completed_order_subject', 10, 2 ); 

function customer_completed_order_subject($string,$order){

$fname = $order->billing_first_name;

$lanme = $order->billing_last_name;

$email = $order->billing_email;

$items = $order->get_items();

foreach($items as $meta_key => $items){

    $product_name = $items['name'];

    $product_id = $items['product_id'];

}

$subject_line = get_field('email_subject',$product_id);

$subject_line = str_replace('{product}',$product_name,$subject_line);

$subject_line = str_replace('{biller_fname}',$fname,$subject_line);

$subject_line = str_replace('{biller_lastname}',$lanme,$subject_line);

$subject_line = str_replace('{biller_email}',$email,$subject_line);

$subject_line = str_replace('{blog_name}',get_bloginfo('name'),$subject_line);

return $subject_line;

}