Mutiple checkbox in php html

I have a form code html like this, but it's error for checkbox question, someone plase help my problem.

if(empty($tampil_pertanyaan)){
                echo "<tr><td colspan=\"6\">Data tidak tersedia</td></tr>";
    }else{
       $no = 1; //for question
       $no2 = 0; //for array
    foreach($tampil_pertanyaan as $row)
   {
    <tr>
        <td><input type="checkbox" class="w3-check" name="ket_jawaban[<?php echo $no2;?>]"  id="ket_jawaban[<?php echo $no2;?>]" value="<?php echo $row->pil1;?>"  oninput="this.className = ''"></td>
        <td> <?php echo $row->pil1;?></td>
    </tr>
    <tr>
        <td><input type="checkbox" class="w3-check" name="ket_jawaban[<?php echo $no2;?>]"  id="ket_jawaban[<?php echo $no2;?>]" value="<?php echo $row->pil2;?>" oninput="this.className = ''"></td>
        <td> <?php echo $row->pil2;?></td>
    </tr>
    <tr>
        <td><input type="checkbox" class="w3-check" name="ket_jawaban[<?php echo $no2;?>]"  id="ket_jawaban[<?php echo $no2;?>]" value="<?php echo $row->pil3;?>" oninput="this.className = ''"></td>
        <td> <?php echo $row->pil3;?></td>
    </tr>
    $no++;
    $no2++;
}

And i my controller (i use Codeigniter)

public function insert_jawaban(){
        // Proses pemvalidasian data yg di input
        $this->form_validation->set_rules('ket_jawaban[]', 'ket_jawaban', 'trim|xss_clean');
        if ($this->form_validation->run() == FALSE){
            echo validation_errors(); // tampilkan apabila ada error
        }else{

            //Insert ke tabel jawaban
            $result = array();
            foreach($_POST['ket_jawaban'] AS $key => $val){

                $result[] = array(
                    "id_jawaban"    => '',
                    "user"          => $_POST['user'][$key],
                    "ket_jawaban"   => $_POST['ket_jawaban'][$key],
                    "id_pilgan"     => $_POST['id_pilgan'][$key],
                    "id_pertanyaan" => $_POST['id_pertanyaan'][$key],
                    "id_survey"     => $_POST['id_survey'][$key],
                    "nama"          => $_POST['nama_user'][$key],
                    "unit"          => $_POST['unit_user'][$key],
                    "jenis"         => $_POST['jenis_user'][$key]
                );
            }

            $res = $this->db->insert_batch('jawaban', $result);
}

why every time I checked always only returns one value, even though I checked three.

before I apologize if there is any wrong in my question is because I am newbie here. Thanks and please be advised