Facebook Messenger API: Post request returning error 500

1. my post webhook:

   router.post('/webhook', function (req, res) { var data = req.body;

         // Make sure this is a page subscription
         if (data.object == 'page') {
           // Iterate
   
    over each entry
   
    // There may be multiple if batched
       data.entry.forEach(function(pageEntry) {
         var pageID = pageEntry.id;
         var timeOfEvent = pageEntry.time;
         // Iterate over each messaging event
         pageEntry.messaging.forEach(function(messagingEvent) {
           if (messagingEvent.optin) {
             receivedAuthentication(messagingEvent);
           } else if (messagingEvent.message) {
             receivedMessage(messagingEvent);
           } else if (messagingEvent.delivery) {
             receivedDeliveryConfirmation(messagingEvent);
           } else if (messagingEvent.postback) {
             receivedPostback(messagingEvent);
           } else if (messagingEvent.read) {
             receivedMessageRead(messagingEvent);
           } else if (messagingEvent.account_linking) {
             receivedAccountLink(messagingEvent);
           } else {
             console.log("Webhook received unknown messagingEvent: ", messagingEvent);
           }
         });
       });
   
       // Assume all went well.
       //
       // You must send back a 200, within 20 seconds, to let us know
       // you've successfully received the callback. Otherwise, the request
       // will time out and we will keep trying to resend.
       res.sendStatus(200);
     }
   });
   
   

2.my receivedMessage function:

function receivedMessage(event) {
  var senderID = event.sender.id;
  var recipientID = event.recipient.id;
  var timeOfMessage = event.timestamp;
  var message = event.message;

  console.log("Received message for user %d and page %d at %d with message:", 
    senderID, recipientID, timeOfMessage);
  console.log(JSON.stringify(message));

  var messageId = message.mid;

  var messageText = message.text;
  var messageAttachments = message.attachments;

  if (messageText) {

    // If we receive a text message, check to see if it matches a keyword
    // and send back the example. Otherwise, just echo the text we received.
    switch (messageText) {
      case 'generic':
        sendGenericMessage(senderID);
        break;

      default:
        sendTextMessage(senderID, messageText);
    }
  } else if (messageAttachments) {
    sendTextMessage(senderID, "Message with attachment received");
  }
}

this is the server log when i run my code with out sendTextMessage which calls the callsend api where i think my code fails:

2017-03-17T10:06:11.296017+00:00 app[web.1]: Received message for user 1367047720019479 and page 1334554393257327 at 1489745171043 with message: 2017-03-17T10:06:11.298010+00:00 app[web.1]: {"mid":"mid.$cAAS9xUXoM5lhDQCaY1a27tcMAHJS","seq":157393,"text":"testing message"} 2017-03-17T10:06:11.298044+00:00 app[web.1]: {"recipient":{"id":"1367047720019479"},"message":{"text":"testing message"}} 2017-03-17T10:06:11.298649+00:00 app[web.1]: POST /webhook/ 200 3.244 ms - 2

now when i include sendtext and callSendAPI:

function sendTextMessage(recipientId, messageText) {
  var messageData = {
    recipient: {
      id: recipientId
    },
    message: {
      text: messageText
    }
  };
console.log(JSON.stringify(messageData));

callSendAPI(messageData);

}


function callSendAPI(messageData) {

 ***console.log("inside the call api");***
request.post({
    uri: 'https://graph.facebook.com/v2.6/me/messages',
    qs: { access_token: access },
    //method: 'POST',
    json: messageData

  }, function (error, response, body) {
    if (!error && response.statusCode == 200) {
      var recipientId = body.recipient_id;
      var messageId = body.message_id;

      console.log("Successfully sent generic message with id %s to recipient %s", 
        messageId, recipientId);
    } else {
      console.error("Unable to send message.");
      console.error(response);
      console.error(error);
    }
  });  
}

this is the output it gives :

2017-03-17T10:09:38.141702+00:00 app[web.1]: Received message for user 1367047720019479 and page 1334554393257327 at 1489745373029 with message: 2017-03-17T10:09:38.141719+00:00 app[web.1]: {"mid":"mid.$cAAS9xUXoM5lhDQOvZVa275xBT7LW","seq":157396,"text":"testing message"} 2017-03-17T10:09:38.141757+00:00 app[web.1]: {"recipient":{"id":"1367047720019479"},"message":{"text":"testing message"}} 2017-03-17T10:09:38.141778+00:00 app[web.1]: inside the call api 2017-03-17T10:09:38.143120+00:00 app[web.1]: POST /webhook/ 500 1.686 ms - 253

please help out how can i fix this error: all tokens set correctly page access and verify token.i am new to the messenger platform

via B.I.G.D