I have "inherited" an event-booking WP plugin and for some reason (apparently, after moving the website into another location of the same server) this is now the situation:

As expected, new reservations are added to the database with the relevant information and can be seen in the custom post type (Bookings) admin page, but...

  • The booking confirmation e-mail only reach registered users (admins) when they make a booking as a test, but not unregistered ones (common visitors) for actual bookings.

  • The notification mail (for "real" bookings by users) to the website owner have a few empty strings instead of the custom field values they should contain.

At the beginning, I though the problem was in wp_mail() usage, so I tried tinkering with it (like, using PHP mail() instead of mailgun SMTP). But looking at this method:

   public static function send_request($booking_id)
    $booking_info = self::get_booking_info($booking_id);
    PC::Debug($booking_info, "booking_info in send_request");
    /* PC::Debug() shows an almost empty array, except for 'event' and 'name' */

    $subject = self::get_title_info($booking_id) . ' - ' . self::$request['subject'][$booking_info['language']];
    $message = self::$request['client'][$booking_info['language']] . self::$footer;
    // Not working = Empty 'To' field
    wp_mail($booking_info['mail'], $subject, $message, self::$headers);

    $subject = self::get_title_info($booking_id) . ' - ' . self::$request['subject']['it'];
    $message = self::$request['admin'] . self::get_info_for_admin($booking_id);
    // Working
    wp_mail(self::admin_mails(), $subject, $message, self::$headers);


Made me realize the only difference seems in the first parameter of wp_mail(), and I have verified (thanks to WP Mail Log plugin) and its raw or JSON format that the "Receiver:" field for these mails is actually empty. This field in "common users" version is derived from:

private static function get_booking_info($booking_id)
$post = get_post( $booking_id );
// Debug is fine

return array(
'name' => $post->post_title,
'event' => MP_Booking_Register::get_event_name($post->booking_show),
'mail' => $post->booking_email,
'language' => $post->booking_language,
'seats' => $post->booking_seats,
'date' => $post->booking_date,

Now, those custom fields are generated by this function:

private static function insert_post($booking_info) {
        $booking = array(
            'post_title'    => $booking_info['name'],
            'post_type'     => 'booking',
            'post_status'   => 'publish',
            'post_date'     => date('Y-m-d H:i:s', strtotime('now')),
            'post_author'   => 1,
        PC::debug($booking_info,"booking_info in insert_post()");
        // Debug OK

        $booking_id = wp_insert_post($booking);
        PC::debug($booking_id,"booking_id (NEW) in insert_post()");
        // Debug OK

        add_post_meta($booking_id, 'booking_first_name', $booking_info['first_name'], true);
        add_post_meta($booking_id, 'booking_last_name', $booking_info['last_name'], true);
        add_post_meta($booking_id, 'booking_email', $booking_info['mail'], true);
        add_post_meta($booking_id, 'booking_language',$booking_info['language'], true);
        add_post_meta($booking_id, 'booking_seats', $booking_info['seats'], true);
        add_post_meta($booking_id, 'booking_show', $booking_info['event'], true);
        add_post_meta($booking_id, 'booking_date', $booking_info['date'], true);
        add_post_meta($booking_id, 'booking_state', 'Richiesto', true);

        $postCustom = get_post_custom($booking_id);
        PC::debug($postCustom, "Custom Fields");

        $allMeta = get_post_meta($booking_id);
        PC::debug($allMeta,"All Post Meta");

        return $booking_id;

Using PC::Debug() I can correctly see $booking_id and $booking_info, but $postCustom and $postMeta are empty arrays. So... Does add_post_meta() fail? If so, why?

Relevant classes:



  • Can you provide a print_r($booking_info); thinking maybe the $booking_id is empty Nov 12, 2017 at 17:38
  • I updated the answer, with some PC::Debug() for PHP Console data.
    – CharlesM
    Nov 13, 2017 at 14:03
  • You can verify by get_post_meta($booking_id); This will show all the meta fields and values that the post_id=$booking_id Nov 13, 2017 at 14:11
  • Yes, I have tried that (you can see it at the end of the last code sample), and the array is empty. Any ideas why? Thank you!
    – CharlesM
    Nov 13, 2017 at 14:16
  • Is there an entry in the wp_posts with the ID of $booking_id with custom post type (Bookings)? Also this $booking_id = wp_insert_post($booking); should be check for returning a valid ID and not WP_ERROR Nov 13, 2017 at 14:19

1 Answer 1



The problem was Database Caching (for casual users) in the W3 Total Cache.

Since most of the meta-data were added "on the fly" to the custom post type structure, they were not immediately accessible to wp_mail() or other methods.

I have now disable DB Caching and the plugin is working fine.

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