Can't add new product to mongodb, having POST 500 error

I'm having trouble on how adding new product to mongodb. I've done the registration side and it's working fine, and so as login. but when I'm adding product I received this message>

POST http://localhost:5000/api/product/newProduct 500 (Internal Server Error)

I double-check my endpoint and I think im right.

dashboard.jsx
import axios from 'axios'
import React, { useEffect, useState } from 'react'
import { useNavigate } from 'react-router'

function Dashboard() {
    const [name, setName] = useState("")
    const [categories, setCat] = useState("")
    const [error, seterror] = useState(false)
    const [data, setData] = useState({})
    const navigate = useNavigate()
    const [price, setprice] = useState(0)

    const handleCat = (e) => {
      setCat(e.target.value.split(','))
    }


    const handleSubmit = async (e) =>{
      e.preventDefault()
      console.log(categories,name,price)
        seterror(false)
        try {
          const prod = await axios.post('http://localhost:5000/api/product/newProduct', {
          name, 
          categories,
          price
          })
          prod.data && navigate('/dashboard')
        } catch (error) {
          seterror(true)
        }
    }
    useEffect(() =>{
      const getProduct = async () =>{
        try {
          const res = await axios.get('http://localhost:5000/api/product')
          setData(res.data)
        } catch (error) {
          
        }
      }
      getProduct()
    },[])

    //console.log(data)

    return (
        <form action="" onSubmit={(e) => handleSubmit(e)}>
        <div>
            <div className="addProductItem">
          <label>Title</label>
          <input
            name="title"
            type="text"
            placeholder="Apple Airpods"
            onChange={(e) => setName(e.target.value)}
          />
        </div>
        <div className="addProductItem">
          <label>Description</label>
          <input
            name="desc"
            type="text"
            placeholder="description..."
            onChange={handleCat}
          />
        </div>
        <div className="addProductItem">
          <label>Price</label>
          <input
            name="price"
            type="number"
            placeholder="100"
            onChange={(e) => setprice(e.target.value)}
          />
          <button >Submit</button>
        </div>
        </div>
        </form>
       
    )
}

export default Dashboard

index.js

const express = require('express')
const mongoose = require('mongoose')
const app = express()
const cors = require('cors')
const dotenv = require('dotenv')
const userRoute = require('./routes/auth')
const productRoute = require('./routes/product')

dotenv.config()

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

mongoose
  .connect(process.env.MONGO_DB)
  .then(() => {
    console.log('Connected to Server')
  })
  .catch((err) => console.log(err))

app.use('/api/auth', userRoute)
app.use('/api/product', productRoute)

app.listen(5000, () => {
  console.log('Local Host is Running 5000')
})

productRoute.js

const router = require('express').Router()
const Product = require('../models/Product')

router.post('/newProduct', async (req, res) => {
  const newProduct = new Product(req.body)

  try {
    const savedProduct = await newProduct.save()
    res.status(200).json(savedProduct)
  } catch (error) {
    res.status(500).json(error)
  }
})


router.get('/', async (req, res) => {
  try {
    const products = await Product.find()
    res.status(200).json(products)
  } catch (error) {
    res.status(500).json(error)
  }
})
module.exports = router

schema

const mongoose = require('mongoose')
const ProductSchema = new mongoose.Schema(
  {
    name: { type: String, required: true, unique: true },
    price: { type: Number, required: true },
    categories: { type: Array },
    img: { type: String },
  },
  { timestamps: true }
)

module.exports = mongoose.model('Product', ProductSchema)