When trying to write a new user to the mongo db i am getting an error when trying to save them to the database i have logged the incoming requests to the console and they all are working properly. If someone could take a look at my code and see what the problem is that would be awesome! Thanks in advance!

app.js

const express = require("express");
const cors = require ("cors");
const passport = require("passport");
const bodyParser = require("body-parser");
const  mongoose  = require("mongoose");
const User = require('./models/user');






var app = express();
app.use(express.json());
app.use(express.urlencoded({extended: true}));
app.use(bodyParser.json());
app.use(cors());
app.use(passport.initialize());
mongoose.connect(process.env.MONGO_URI, (err,res)=>{
    if(err){
        console.log("not connected to mongo")
    }else{
        console.log("connection successful")
    }
})


app.post("/user/signup", (res,res)=>{
    let newUser = new User({
        firstName: req.body.firstName,
        lastName: req.body.lastName,
        email: req.body.email
    })
    newUser.save()
})






app.listen( 8080, () =>{
    console.log(`Server is listening on port: 8080`)
})

mongoose model:

const mongoose = require('mongoose');


new userSchema = new mongoose.Schema({
    firstName: string,
    lastName: string,
    email: string
})


module.exports = (userSchema)

console.log when starting server: