facebook messeger bot api cu js nod trimite mai multe raspunsuri

Am o eroare cu api mesajul bot. Din anumite motive, înflăcărează mai multe ca 20 la un moment dat de mesaje la un anumit utilizator. Sunt folosind Heroku pe nod. Nu am indiciu de ce face acest lucru? Orice ajutor ar fi mult mai apreciat.

use strict;
var express = require(express);
var app = express();
var bodyParser = require('body-parser');
var request = require('request');

app.use(bodyParser.json());

app.get('/', function(req, res){

   res.send('hello'); 

});


app.get('/webhook', function (req, res) {
    if (req.query['hub.verify_token'] === 'my_voice_is_my_password_verify_me') {
        res.send(req.query['hub.challenge'])
    }
    res.send('Error, wrong token')
})
app.post('/webhook', function (req, res) {
    let messaging_events = req.body.entry[0].messaging;
    for (let i = 0; i < messaging_events.length; i++) {
        let event = req.body.entry[0].messaging[i]
        let sender = event.sender.id
        if (event.message && event.message.text) {
            let text = event.message.text
            sendTextMessage(sender, Text received, echo:  + text.substring(0, 200))
        }
    }
    res.sendStatus(200)
})

function sendTextMessage(sender, text) {
    let messageData = { text:text }
    request({
        url: 'https://graph.facebook.com/v2.6/me/messages',
        qs: {access_token: process.env.PAGE_ACCESS_TOKEN},
        method: 'POST',
        json: {
            recipient: {id:sender},
            message: messageData,
        }
    }, function(error, response, body) {
        if (error) {
            console.log('Error sending messages: ', error)
        } else if (response.body.error) {
            console.log('Error: ', response.body.error)
        }
    })
}







app.listen(process.env.PORT || 8080);