Cakephp 4 giving 403 error while using ajax - ajax

Question

I am trying to implement cascading drop down box in cakephp 4 using ajax.
I'm getting an 403 error has tried many solutions from google and stack overflow from htaccess till syntax error and logical error can anyone please help trying since long.
Here is my code:
Add.php
<?php echo $this->Form->control('groups',['options' => $groups],array('id'=>'GroupId'));
echo $this->Form->input('user_id',array('id'=>'UsersId'));
?>
<?= $this->Form->button(__('Submit'),array('id'=>'post')) ?>
<?= $this->Form->end() ?>
<?php echo $this->Html->script('//ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js');?>
<script type="text/javascript" >
$(document).ready(function(){
$("#groups").change(function(){
var deptid = $(this).val();
//var path="<?php echo $this->Url->webroot ?>/Users/getbygroup";
$.ajax({
url: '../Users/getbygroup',
type: 'POST',
data: deptid,
dataType: 'json',
cache: false,
contentType: false,
success:function(response){
var len = response.length;
$("#UserId").empty();
for( var i = 0; i<len; i++){
var id = response[i]['id'];
var name = response[i]['name'];
$("#UserId").append("<option value='"+id+"'>"+name+"</option>");
}
}
});
});
});
</script>
Add action in files controller:
public function add()
{
$this->loadModel('Users');
$this->loadModel('Groups');
$this->set('groups', $this->Groups->find('list'));
$result = $this->Users->find('all'); // returns query object
$data = $result->toArray(); // converts query object to key value array
$file = $this->Files->newEmptyEntity();
if ($this->request->is('post')) {
$file = $this->Files->patchEntity($file, $this->request->getData());
if ($this->Files->save($file)) {
$this->Flash->success(__('The file has been saved.'));
return $this->redirect(['action' => 'index']);
}
$this->Flash->error(__('The file could not be saved. Please, try again.'));
}
$this->set(compact('file'));
}
getbygroup function in users controller:
public function getbygroup() {
$fname= $this->request->getData('deptid');
$this->viewbuilder()->layout = 'ajax';
$users = $this->Users->find('list', array(
'conditions' => array('Users.group_id' => $fname),
'recursive' => -1));
$this->set('users', $users);
}