title: Missing required parameters, includes an invalid parameter value, parameter more than once with LinkedIn API
body: <p>I try to authenticate with LinkedIn API with OAuth2. Code:</p>
  
  <pre><code>if ((isset($_GET["code"])) AND (isset($_GET["state"]))) {
          $code = $_GET["code"];
          $state = $_GET["state"];
  
          $curl_request = curl_init();
          curl_setopt_array($curl_request, array(
              CURLOPT_RETURNTRANSFER =&gt; 1,
              CURLOPT_URL =&gt; "https://www.linkedin.com/uas/oauth2/accessToken",
              CURLOPT_POST =&gt; 1,
              CURLOPT_POSTFIELDS =&gt; array(
                  grant_type =&gt; "authorization_code",
                  code =&gt; "$code",
                  redirect_uri =&gt; "SECRET",
                  client_id =&gt; "SECRET",
                  client_secret =&gt; "SECRET"
              )
          ));
  
          $curl_result = curl_exec($curl_request);
  
          var_dump($curl_result);
  
  }
  </code></pre>
  
  <p>I got this message:</p>
  
  <blockquote>
    <p>string(153) "{"error_description":"missing required parameters,
    includes an invalid parameter value, parameter more than once. :
    client_id","error":"invalid_request"}"</p>
  </blockquote>
  
  <p>Could you help m?</p>