dropbox isn't sending webhooks

what i tried

the below code is my webhook endpoint

- it responds to the validation request

- and it generates and stores a timestamp into a file called "GTest.txt" each time a request is sent to this function/corresponding route

  public function webhook_endpoint()
  {
    $report_object = new report;
    $result = "";
    $file_content_prefix = "";

    if (isset($_GET['challenge'])) {
      $result = $_GET['challenge'];
      $file_content_prefix = "Challange";
    } elseif ($report_object->webhook_endpoint_authenticate() == 1) {
      $file_content_prefix = "Authenticated";
    } else {
      header('HTTP/1.0 403 Forbidden');
      $file_content_prefix = "Not authenticated";
    }

    $timestamp = date('Y-m-d h:i:s a', time());
    $file_content =  $file_content_prefix." ".$timestamp;
    $file_name = "GTest.txt";
    file_put_contents($file_name, $file_content);

    return $result;
  }

problem

- It validates and generates a timestamp for that request just fine

- but when i change a file in the app's dropbox folder it doesnt generate any new timestamps in my "GTest.txt" file which leads me to believe no webhook request was sent

- i'm editing the dropbox file both on my desktop and on dropbox online (i edited a test files content and name and also added a .png file) but no webhook request seemed to have sent. :(

P.s

is this a glitch? if so please explain why this kind of glitch would happen?