将自定义用户电子邮件添加到 CC 以获取特定的 Woocommerce 电子邮件通知

In Woocommerce I try to customize the code from this thread to add a custom email as "CC" email address in customer completed order email notification:

/**
 * Function adds a BCC header to emails that match our array
 * 
 * @param string $headers The default headers being used
 * @param string $object  The email type/object that is being processed
 */
    function add_cc_to_certain_emails( $headers, $object ) {
    // email types/objects to add cc to
    $cc_email = get_user_meta( $user_id, 'order_cc_email', true ); // MY CUSTOM CODE
    $add_cc_to = array(
        'customer_completed_order', // Customer Processing order from WooCommerce
    );
    // if our email object is in our array
    if ( in_array( $object, $add_cc_to ) ) {
        // change our headers
        $headers = array( 
            $headers,
//          'Cc: Me <me@example.com>' ."
", // INITIAL CODE
            'Cc: '.$cc_email.' <'.$cc_email.'>' ."
", // MY CUSTOM CODE
    }
    return $headers;
}
add_filter( 'woocommerce_email_headers', 'add_cc_to_certain_emails', 10, 2 );

我找不到从用户元数据中获取自定义用户电子邮件的方法，因此我的代码无法按预期工作.

add_filter( 'woocommerce_email_headers', 'custom_cc_email_headers', 10, 3 );
function custom_cc_email_headers( $header, $email_id, $order ) {

    // Only for "Customer Completed Order" email notification
    if( 'customer_completed_order' !== $email_id )
        return $header;

    // Get the custom email from user meta data  (with the correct User ID)
    $custom_user_email = get_user_meta( $order->get_user_id(), 'order_cc_email', true );

    if( ! empty($custom_email) ) 
        return $header; // Exit (if empty value)

    // Get customer billing full name
    $user_name  = $order->get_billing_first_name().' ';
    $user_name .= $order->get_billing_last_name();

    // Merge and prepare the data
    $formatted_email = utf8_decode($user_name . ' <' . $custom_user_email . '>');

    // Add Cc to headers
    $header .= 'Cc: '.$formatted_email .'
';

    return $header;
}