// ************ creating new accounts when receiving new viewing booking ***********
function processViewingBooking($vars) {
    require_once(ABSPATH . WPINC . '/registration.php');
    $username =  $vars['booked_by'];
    $useremail = $username;
    $address = $vars['address'];
    if($username && $address) {
        // create account if necessary
        $user_id = username_exists( $username );
        if ( !$user_id ) {
            $random_password = wp_generate_password( 12, false );
            $user_id = wp_create_user( $username, $random_password, $useremail );
            echo "account created: ".$user_id;
        } else {
            echo "account identified: ".$user_id;
        }
        // store event
        $new_event = array();
        $new_event['post_title'] = time();
        $new_event['post_type'] = 'viewings';
        $new_event['post_content'] = 'This is my new viewing.';
        $new_event['post_status'] = 'publish';
        $new_event['post_author'] = $user_id;
        $event_id = wp_insert_post($new_event);
        if($event_id) {
            update_post_meta($event_id, "address", $address);
        }
    } else {
        // fail silently
        echo "please send username and address parameters";
    }
}

// ************ end creating new accounts when receiving new viewing booking ************