Bug Agenda Sekolah

public function get_agenda_sekolah() {
      $start = substr($this->input->get("start"), 0, 10);
      $end = substr($this->input->get("end"), 0, 10);
      $data = [];
      if (is_valid_date($start) && is_valid_date($end)) {
         $query = $this->db->query("
            SELECT post_title AS title
               , post_date AS `start`
            FROM posts
            WHERE post_type='agenda'
            AND post_date BETWEEN '$start' AND '$end'
         ");

         foreach ($query->result() as $row) {
               $data[] = [
                  'title' => $row->title,
                  'start' => $row->start
               ];
         }
      }
      echo json_encode($data);
   }