Can't Get Access Token In Wordpress

[TendiF]

I can't get the token even i click allow

use Kunnu\Dropbox\Dropbox;
use Kunnu\Dropbox\DropboxApp;
//Dropbox author
add_action('wp_ajax_dropbox_user_getauth', 'dropbox_user_getauth');
function dropbox_user_getauth(){
  // echo 'Dropbox Auth';
  session_start();
  require_once(plugin_dir_path(__FILE__).'vendor/autoload.php');

  //Configure Dropbox Application
  $app = new DropboxApp("xxxxxxxxx", "xxxxxxxxxxx");

  //Configure Dropbox service
  $dropbox = new Dropbox($app);
  //DropboxAuthHelper
  $authHelper = $dropbox->getAuthHelper();
  //Callback URL
  $callbackUrl = "https://dev.audiotext.com/wp-admin/admin-ajax.php?action=dropbox_user_getauth";
   // var_dump($authHelper);
   //Fetch the Authorization/Login URL
   $authUrl = $authHelper->getAuthUrl($callbackUrl);

   echo "<a target='_blank' href='" . $authUrl . "'>Log in with Dropbox</a>";

   if (isset($_GET['code']) && isset($_GET['state'])) {
    //Bad practice! No input sanitization!
    $code = $_GET['code'];
    $state = $_GET['state'];

   //Fetch the AccessToken
   $accessToken = $authHelper->getAccessToken($code, $state, $callbackUrl);

   echo $accessToken->getToken();
  }
}

someone know what my fault

i used localhost https anyway
==========HERE MY ERROR LOG====================
// if ($tokenInStore !== $csrfToken) {
// throw new DropboxClientException("Invalid CSRF Token. CSRF Token Mismatch.");
// }
AFTER I REMOVE THAT DECISION I GET TOKEN AND IT CAN BE USE 🤣