ทำ chart mixed ให้แสดงโชว์ข้อมูลออกมาเป็นกราฟ แต่ปัญหาตอนนี้เส้นกราฟไม่ขึ้น

 <div class="col-md-8">
          <canvas id="mixed-chart" width="800" height="450"></canvas>
          <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.min.js"></script>
          <div class="form-group">
            <script>
              new Chart(document.getElementById("mixed-chart"), {


                type: 'bar',
                data: {
                  labels: [

                    <?php

                    for ($i = 1; $i <= $lastDayThisMonth; $i++) {
                      if ($i > 1) {
                        echo ',';
                      }
                      echo "'" . $i . "'";
                    } ?>

                  ],
                  datasets: [{
                    label: "total_prepaid",
                    type: "line",
                    borderColor: "#8e5ea2",
                    data: [
                      <?php
                      $k = [];
                      foreach ($day_total_prepaid_chart as $row) {
                        $k[($row->no_date * 1)] = $row->total_prepaid;
                      }
                      for ($j = 1; $j <= $lastDayThisMonth; $j++) {
                        if ($j > 1) {
                          echo ',';
                        }
                        echo (isset($k[$j])) ? "'" . $k[$j] . "'" : "'0'";
                      }
                      ?>
                    ],
                    fill: false
                  },/* {
                    label: "Africa",
                    type: "line",
                    borderColor: "#3e95cd",
                    data: [133, 221, 783, 2478],
                    fill: false
                  }, {
                    label: "Europe",
                    type: "bar",
                    backgroundColor: "rgba(0,0,0,0.2)",
                    data: [408, 547, 675, 734],
                  }, {
                    label: "Africa",
                    type: "bar",
                    backgroundColor: "rgba(0,0,0,0.2)",
                    backgroundColorHover: "#3e95cd",
                    data: [133, 221, 783, 2478]
                  }*/]
                },
                options: {
                  title: {
                    display: true,
                    text: 'Population growth (millions): Europe & Africa'
                  },
                  legend: {
                    display: false
                  }
                }
              });
            </script>

 public function get_dashboard_day_total_prepaid_chart()
  {
$sql = "SELECT MONTHNAME(airwaybills.date) as month, sum(airwaybills.total_prepaid) as total_prepaid, DATE_FORMAT(airwaybills.date, '%d') as no_date, 
   date(airwaybills.date) as date, customers.shipper_name as cus_shipname, customers.consignee_name as cus_conname,airport_departures.short_name AS dep_name,
   airport_destinations.short_name as des_name, airwaybills.pieces as air_pieces,
   MONTHNAME(airwaybills.created_at) as namemonth from airwaybills 
   INNER JOIN airport_departures ON airwaybills.airport_departure_id = airport_departures.id 
   INNER JOIN airport_destinations ON airwaybills.airport_destination_id = airport_destinations.id 
   INNER JOIN customers ON airwaybills.customer_id = customers.id 
   WHERE airwaybills.customer_id = customers.id 
   GROUP BY MONTHNAME(airwaybills.date),date(airwaybills.date)";   

   //  $query = $this->db->get();
   $query = $this->db->query($sql);
   //echo "<pre>";
   // print_r($query->result());
   // echo "</pre>";die();
  return $query->result_array();

public function index()
  {
    $user = $this->ion_auth->user()->row();
    $user_group = $this->users_group_model->find_userId($user->user_id);

    // echo '<pre>',print_r($user_group,1),'</pre>';
    if ($user_group->group_id == 1) {
      $chargeable_weight_chart = $this->dashboard_model->get_dashboard_chargeable_weight_chart();
      // $day_total_prepaid_chart = $this->dashboard_model->get_dashboard_day_total_prepaid_chart();
      $total_prepaid_chart = $this->dashboard_model->get_dashboard_total_prepaid_chart();
      $pieces_chart = $this->dashboard_model->get_dashboard_pieces_chart();
      $total_chart = $this->dashboard_model->get_dashboard_total_chart();

    /*  $start_date     = isset($_POST['start_date']) ? $_POST['start_date'] : "";
      $end_date       = isset($_POST['end_date']) ? $_POST['end_date'] : "";
      $departure      = isset($_POST['departure']) ? $_POST['departure'] : "";
      $destination    = isset($_POST['destination']) ? $_POST['destination'] : "";*/

      $day_total_prepaid_chart = $this->dashboard_model->get_dashboard_day_total_prepaid_chart();

      $lastDayThisMonth = date("t");

      $this->data['day_total_prepaid_chart'] = $day_total_prepaid_chart;
      $this->data['lastDayThisMonth'] = $lastDayThisMonth;

      $this->data['chargeable_weight_chart'] = $chargeable_weight_chart;
      $this->data['total_prepaid_chart'] = $total_prepaid_chart;
      $this->data['pieces_chart'] = $pieces_chart;
      $this->data['total_chart'] = $total_chart;

      $this->data['view_name'] = 'dashboards/index';
    } else
      $this->data['view_name'] = 'dashboards/index_welcome';

    $this->load->view('layouts/main', $this->data);
  }