How can I use Dialogflow-fulfillment library while utilizing the serverless architecture?

Question

I'm setting up a lambda function using serverless that will be invoked through a Webhook in Google's NLP Dialogflow. My end goal is to be able to use the dialogflow-fulfillment library.

I have tried reinstalling node_modules by doing "npm install ..." to all the required modules. The package.json has all dependencies require.. using npm init.

// handler.js

const debug = require('debug')('http');
const express = require('express')
const sls = require('serverless-http');
const app = express();
app.get('/', async (req, res, next) => {
    //console.log(req + res);
    const { WebhookClient } = require('dialogflow-fulfillment')
    const agent = new WebhookClient({ req, res });

    function justSayHi(agent) {
        console.log(`Something's happening`);
        agent.add('Hello from dialogflow-fulfillment');
    }
    let intentMap = new Map();
    intentMap.set('justsayhi', justSayHi);
    agent.handleRequest(intentMap);

    console.log("webhook called")
});
module.exports.server = sls(app);

When printing the logs in the command prompt sls logs -f app, I get the following error message:

"Unable to import module 'app': Error
    at Function.Module._resolveFilename (module.js:547:15)
    at Function.Module._load (module.js:474:25)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)"

Again, my end goal is to be able to use Dialogflow-fulfillment library utilizing the serverless architecture.

I'm wondering why it's saying unable to import module app.

I'm open to restructuring how I have this set up also, I have not found a good way to do this so far.