Post checkbox values then encode to json

I want to create network graph with checkboxes. If I click a data's button, it shows where this data is connected to. If I select 1 or more, I want to print the original data node (it's working), and the selected nodes. My idea is to post the checkbox, the button and the td to that PHP file where I encode it to JSON, but it's not working. Now if I click the button, the modal disappear.

How can I post the checkbox and the td values to another PHP file to encode it to JSON?

Checkbox

$output .='<form name="relationCheck" action="nodes.php" method="post">';

            while($row=$result->fetch_assoc()){ 

                $output .='

                <tr>  
                    <td align="center"><input name="id[]" class="checkboxes" type="checkbox" value="'.$row["id2"].'"</td>
                    <td>'.$row["data"].'</td>  
                </tr>  
            ';
while($row = $result3->fetch_assoc()){
            $output .= '<input type="button" name="submit" id="'.$row["data_id"].'" value="view" class="btn btn-success relations">';
            }
            $output .= '</form>';

nodes.php

$id2=$_POST['id'];

        if(isset($id2)){

            $sql2=$conn->prepare("SELECT id, data
                FROM table1
                WHERE id=?
                GROUP BY id");

            $sql2 -> bind_param('i', $id2);
            $sql2 -> execute();
            $result2 = $sql2 -> get_result();
            $sql2 -> close();

            while($row = mysqli_fetch_assoc($result2)){
                $id2 = $row['id'];
                $data = $row['data'];


                $arr[] = array("id" => $id2,
                    "label" => $data);
            } 


        echo json_encode($arr);