Как использовать материалы Discord.JS в Express

Привет, я пытаюсь создать API в Express, и я не знаю, как использовать этот var user = client.fetchUser(req.params.userId).catch(res.send('<pre>500 internal server error</pre>')) внутри Express, он просто возвращает эту ошибку:

(node:33064) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:482:11)
    at ServerResponse.header (M:\JS Bot\Outh\api\node_modules\express\lib\response.js:767:10)
    at ServerResponse.contentType (M:\JS Bot\Outh\api\node_modules\express\lib\response.js:595:15)
    at ServerResponse.send (M:\JS Bot\Outh\api\node_modules\express\lib\response.js:145:14)
    at app.get (M:\JS Bot\Outh\api\app.js:20:9)
    at Layer.handle [as handle_request] (M:\JS Bot\Outh\api\node_modules\express\lib\router\layer.js:95:5)
    at next (M:\JS Bot\Outh\api\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (M:\JS Bot\Outh\api\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (M:\JS Bot\Outh\api\node_modules\express\lib\router\layer.js:95:5)
    at M:\JS Bot\Outh\api\node_modules\express\lib\router\index.js:281:22
(node:33064) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:33064) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Код ниже:

const express = require('express')
const { Client, RichEmbed } = require('discord.js');
const yt = require('ytdl-core');
const ffmpeg = require('ffmpeg');
const fs = require('fs');
const Discord = require('discord.js');
const ytapi = require('simple-youtube-api');
const app = express()
const port = 80

const client = new Discord.Client();
client.login("NTQwXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");

app.get('/', async (req, res) => {
    res.send('hi test')
})

app.get('/user/:userId', async (req, res) => {
    var user = client.fetchUser(req.params.userId).catch(res.send('<pre>500 internal server error</pre>'))
    res.send(`User grabbed was ${user}`).catch(console.error)
})

app.listen(port, () => console.info(`App listening on port ${port}!`))

Есть ли способ исправить это.

Спасибо, Эндер