Node/Express endpoint to send sms to multiple users

twilio.js

const Router = require('express').Router;
const router = new Router();
const client = require('twilio')('xxxxxxx', 'xxxxx');

router.post('/send-sms', function(req, res){
    var users = req.body.users
    var smsBody = req.body.smsBody;

    async.each(users, function(user, callback) {
        client.sendMessage({
                to: user.cellNum,
                from: '+15005550006',
                body: smsBody

            }, function(err) {
                if (!err) { 
                    return callback();
                }
                else{
                    return callback(err);
                }
            });
    }, function(err){
        if(err){
            res.status(500).json({
                msg: err.message
            });
        }
        else{
            res.json({
                msg: "Message sent to all users successfully"
            });
        }
    })
})