title: session data empty on the payment gateway return URL in Codeigniter
body: <p>There are several questions on this issue and I have tried most of the solutions suggested there, still I am unable to figure out the issue. I am using PayU payment API. Upon successful payment, the session data is empty on the RETURN URL. I had set only few fields in the session like user ID, product IDs in the cart</p>
  <p>Below is the return URL function:</p>
  <pre><code>public function payment_success() {
      echo &quot;&lt;pre&gt;&quot;; print_r($_SESSION);
      exit;
  }
  </code></pre>
  <p>The output I see:</p>
  <pre><code>    Array
  (
      [__ci_last_regenerate] =&gt; 1600755715
  )
  </code></pre>
  <p>Note that the session data persists while redirecting from function to function. Issue is only on the payment gateway's return URL function which is also in the same controller</p>
  <p>PHP Version:7.2.31
  Codeigniter Version:3.1.11</p>
  <p>//My config.php:</p>
  <pre><code>$config['sess_driver'] = 'files';
  $config['sess_cookie_name'] = 'ci_session';
  $config['sess_expiration'] = 0;
  $config['sess_save_path'] = NULL;
  $config['sess_match_ip'] = FALSE;
  $config['sess_time_to_update'] = 300;
  $config['sess_regenerate_destroy'] = FALSE;
  </code></pre>
  <p>Possibilities I have tried as suggested</p>
  <pre><code>//1
  $config['sess_save_path'] = APPPATH.'ci_session/';
  
  //2
  $config['sess_expiration'] = 7200;
  
  //3 in Session.php
  // ini_set('session.name', $params['cookie_name']);
  ini_set('session.id', $params['cookie_name']);
  
  //4 tried under PHP versions 7.1 and 7.3
  </code></pre>