Facebook Messenger API "URL COULD NOT BE VALIDATED"

Question

I'm trying to setup the Facebook messenger API and I'm getting this error when I attempt to add the WebHook:

The URL couldn't be validated. Callback verification failed with the following errors: curl_errno = 60; curl_error = SSL certificate problem: unable to get local issuer certificate; HTTP Status Code = 200; HTTP Message = Connection established

I've setup my NodeJS server using the code they provided in the tutorial. Here's the url: https://stackoverload.me/chatter/webhook

EDIT HERE'S THE RESOLUTION (someone wanted to see the code):

var express = require('express');

var fs = require('fs');
var https = require('https');

var app = express();
app.use(express.static('public'));

// SSL
https.createServer(
    {
        ca: fs.readFileSync(__dirname + '/server.ca'),
        key: fs.readFileSync(__dirname + '/server.key'),
        cert: fs.readFileSync(__dirname + '/server.cert')
    }
, app).listen(443, function() {
    console.log('Server is now running.');
});

// HTTP redirect to SSL
express()
    .get('*', function(req,res){
        res.redirect('https://example.com' + req.url)
    })
    .listen(80);

Answer 1

Forgot to answer this, but I found out that I added a ca file and parameter to my https server and Facebook then accepted it.