title: How to get the PSID after user clicked the SEND-TO-MESSENGER button?
body: <p>This is my code:</p>
  
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    </p>
  
  <pre><code>window.fbAsyncInit = function() {
    FB.init({
      appId: "xxx",
      xfbml: true,
      version: "v2.6"
    });
  
    FB.Event.subscribe('send_to_messenger', function(response) {
     // callback for events triggered by the plugin
       console.log('inside the send_to_messenger'); 
       if ( response.event == 'clicked' ) {
  
       };
  
  
    });
  
  };
  
  (function(d, s, id){
     var js, fjs = d.getElementsByTagName(s)[0];
     if (d.getElementById(id)) { return; }
     js = d.createElement(s); js.id = id;
     js.src = "//connect.facebook.net/en_US/sdk.js";
     fjs.parentNode.insertBefore(js, fjs);
  }(document, 'script', 'facebook-jssdk'));
  </code></pre>
  
  <p></p>
  
  <p>
     </p>
  
  <p>
  </p>
  
  <p>So now, how do I get the PSID of the user ?</p>