Storing Data into MongoDB is failing

I am new to the MERN stack and I want to store user information into the MongoDB which has two string attributes "name" and "role".

I am getting an error in the browser console which states "Failed to load resource: Request timeout" and "Unhandled Promise Rejection: AxiosError: timeout exceeded"

server index.js

const express = require("express");
const mongoose = require("mongoose");
const cors = require("cors"); 
app = express();

const bookModel = require("./models/book");
const userModel = require("./models/user"); 

app.use(express.json());
app.use(cors);  

// mongoose.connect('mongodb://mh_user:<credentials>').then(() => {console.log('test')});

mongoose.connect("mongodb://mh_user:<credentials>", {
    useNewUrlParser: true,
})

// usermodel

app.postUser("/insert", async (req, res) => {

    const userName = req.body.userName
    const role = req.body.role
    const user = new userModel({ username: userName, role: role })

    try {
        await userModel.save();
    } catch (err) {
        console.log(err);
    }
});

app.getUser("/read", async (req, res) => {
    userModel.find({}, (err, result) => {
        if(err) {
            res.send(err)
        } 
        res.send(result)
    })
});


// bookmodel
app.post("/insert", async (req, res) => {

    const bookName = req.body.bookName
    const ISBN = req.body.ISBN
    const book = new bookModel({ bookname: bookName, ISBN: ISBN })

    try {
        await bookModel.save();
    } catch (err) {
        console.log(err);
    }
});

app.get("/read", async (req, res) => {
    bookModel.find({}, (err, result) => {
        if(err) {
            res.send(err)
        } 
        res.send(result)
    })
});

app.listen(3001, () => {
    console.log("Server running on port 3001 ...");
})

client adduser.js

import styles from './Home.module.css'
import React, { useState } from "react";
import Axios from "axios"

export default function AddUser() {
    const [userName, setUserName] = useState("");
    const [role, setRole] = useState("");

    const addToDatabase = () => {
        Axios.post("http://localhost:3001/insert", { userName: userName, role: role })
    }

    return (
        <div className={styles.container}>

            <main className={styles.main}>
                <h1 className={styles.title}>
                    Fügen Sie einen <a>neuen Nutzer</a> hinzu
                </h1>

                <p className={styles.description}>
                    Create - Operation{' '}
                </p>

                <div className={styles.grid}>
                    <form className={styles.table}>
                        <label>
                            <input
                                onChange={(event) => {
                                    setUserName(event.target.value);
                                }}
                                type="name" placeholder='name'
                            />
                        </label>
                        <label>
                            <input
                                onChange={(event) => {
                                    setRole(event.target.value);
                                }}
                                type="role" placeholder='role'
                            />
                        </label>
                    </form>
                </div>
                <br></br>
                <button
                    onClick={addToDatabase}
                >speichern</button>
                <br></br>
                <a href="http://localhost:3000/">
                    <button>Hauptmenü</button>
                </a>
            </main>

            <footer className={styles.footer}>
                <a>
                    Powered by{' '}- Gruppe 1
                </a>
            </footer>

        </div>
    );
}

server user.js

const mongoose = require('mongoose'); 

const userSchema = new mongoose.Schema({
    name: {
        type: String, 
        required: true,
    }, 
    role: {
        type: String, 
        required: true,
    }
}); 

const user = mongoose.model('userData', userSchema)
module.exports = user