Facebook Messenger bot not sending messages in order

Question

I'm playing around with building a simple Facebook Messenger chatbot and I'm having trouble sending messages in sequence.

In the example above, it should have printed "Hello!", "1", "2", "3" in order. I'm currently following the Facebook docs found here to implement this simple text message function. I've included my Express Node.JS server code below:

Defining the sendTextMessage() function:

var request = require("request");
function sendTextMessage(user, text) {
    messageData = {
        text: text
    };
    request({
        url: "https://graph.facebook.com/v2.6/me/messages",
        qs: {access_token: PAGE_ACCESS_TOKEN},
        method: "POST",
        json: {
            recipient: {id: user},
            message: messageData
        }
    }, function(error, response, body) {
        if (error) {
            console.log("Error sending message: ", error);
        } else if (response.body.error) {
            console.log("Error: ", response.body.error);
        } else {
            console.log("Message successfully send.")
        }
    });
}

Using it to send a response:

sendTextMessage(user, "Hello!");
sendTextMessage(user, "1");
sendTextMessage(user, "2");
sendTextMessage(user, "3");

I even tried implementing a simple queue that queues messages and only sends one message at a time after each request's success callback. This is making me suspect that I'm not interacting with the Messenger API correctly.

Has anyone encountered this issue? How can I get messages to send in sequence? Thanks!

EDIT

Because I implemented a simple queue but still experiencing this problem, I'm including the code for my simple queue system here.

var queue = [];
var queueProcessing = false;

function queueRequest(request) {
    queue.push(request);
    if (queueProcessing) {
        return;
    }
    queueProcessing = true;
    processQueue();
}

function processQueue() {
    if (queue.length == 0) {
        queueProcessing = false;
        return;
    }
    var currentRequest = queue.shift();
    request(currentRequest, function(error, response, body) {
        if (error || response.body.error) {
            console.log("Error sending messages!");
        }
        processQueue();
    });
}

queueRequest(/* Message 1 */);
queueRequest(/* Message 2 */);
queueRequest(/* Message 3 */);

UPDATE

This "bug" was reported to Facebook but it sounds like they aren't going to fix it. Please read the ticket thread on Facebook's post here for details on what they say is going on. (Thank you to Louise for getting Facebook's attention on this)

Answer 1

I submitted a bug report to Facebook about this because I was having the same problem. They acknowledged that it is indeed a bug and are working to fix it: https://developers.facebook.com/bugs/565416400306038

Answer 2

After you send a POST to /me/messages, you'll receive a response that has a message id (mine start with 'mid.' which maybe stands for message id?):

{ recipient_id: '1015411228555555',
  message_id: 'mid.1464375085492:b9606c00ca33c12345' }

After being completely received by the FB Messenger API, you'll get a call to your webhook (with no message events) that confirms receipt:

{ sender: { id: '1015411228555555' },
  recipient: { id: '566031806XXXXXX' },
  delivery:
   { mids: [ 'mid.1464375085492:b9606c00ca33c12345' ],
     watermark: 1464375085604,
     seq: 176 } }

I think that delivery receipt is the best way to ensure delivery, then send the next message.