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
            sendToApiAi(sender, text.substring(0, 200))
        }
    }
    res.sendStatus(200)
})