title: Facebook Chat bot (PHP webhook) sending multiple replies
body: <p>My Facebook chat bot is working but it's sending back multiple messages after my initial message to it. This is my webhook script (i appreciate it's a very rough working example):</p>
  
  <pre><code>$challenge = $_REQUEST['hub_challenge'];
  $verify_token = $_REQUEST['hub_verify_token'];
  
  if ($verify_token === 'MY_VERIFICATION_TOKEN') {
    echo $challenge;
  }
  
  $input = json_decode(file_get_contents('php://input'), true);
  
  $sender = $input['entry'][0]['messaging'][0]['sender']['id'];
  $message = $input['entry'][0]['messaging'][0]['message']['text'];
  
  
  //API Url
  $url = 'https://graph.facebook.com/v2.6/me/messages?access_token=&lt;my-token&gt;';
  
  //Initiate cURL.
  $ch = curl_init($url);
  
  //The JSON data.
  $jsonData = '{
      "recipient":{
          "id":"'.$sender.'"
      }, 
      "message":{
          "text":"Hey Lee!"
      }
  }';
  
  //Encode the array into JSON.
  $jsonDataEncoded = $jsonData;
  
  //Tell cURL that we want to send a POST request.
  curl_setopt($ch, CURLOPT_POST, 1);
  
  //Attach our encoded JSON string to the POST fields.
  curl_setopt($ch, CURLOPT_POSTFIELDS, $jsonDataEncoded);
  
  //Set the content type to application/json
  curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
  
  //Execute the request
  $result = curl_exec($ch);
  </code></pre>