title: Graph returned an error: Invalid appsecret_proof provided in the API argument
body: <p>i am using facebook PHP sdk (v4) to fetch user information,
  after installing SDK, i add the code</p>
  
  <pre><code>$fb = new Facebook\Facebook([
    'app_id' =&gt; 'my app id',
    'app_secret' =&gt; 'my app secret',
    'default_graph_version' =&gt; 'v2.5',
  ]);
  
  try {
    // Returns a `Facebook\FacebookResponse` object
   $access_token= //copied from my https://developers.facebook.com/tools/explorer/
    $response = $fb-&gt;get('/me?fields=id,name', '$access_token');
  } catch(Facebook\Exceptions\FacebookResponseException $e) {
    echo 'Graph returned an error: ' . $e-&gt;getMessage();
    exit;
  } catch(Facebook\Exceptions\FacebookSDKException $e) {
    echo 'Facebook SDK returned an error: ' . $e-&gt;getMessage();
    exit;
  }
  
  $user = $response-&gt;getGraphUser();
  
  echo 'Name: ' . $user['name'];
  </code></pre>
  
  <p>but when i run the page it gives me this error, </p>
  
  <pre><code>Graph returned an error: Invalid appsecret_proof provided in the API argument
  </code></pre>
  
  <p>i am copying the app secret correctly, what could be the reason for such error and how should i fix this ? </p>