Failed to load resource: the server responded with a status of 500 (Internal Server Error) , Unexpected token ‘P’, “Proxy erro”… is not valid JSON

[ i have question in the end]

Failed to load resource: the server responded with a status of 500 (Internal Server Error)
App.jsx:18 Error fetching todos: SyntaxError: Unexpected token ‘P’, “Proxy erro”… is not valid JSON

this is the error statement

what I understand is that its a internal server error in my code

this is the route.js

const express = require("express")

const router = express.Router();

// // get todo
router.get("/todos",(req,res)=>{
      res.status(200).json({mssg:"GET REQUEST TO /api/todos"})
});


// post todo
router.post("/todos",(req,res)=>{
      res.status(201).json({mssg:"GET REQUEST TO /api/todos"})
});



//delete todo
router.delete("/todos/:id",(req,res)=>
{
    res.status(200).json({mssg:"DELETE REQUEST TO /api/todos/:id"});
});


//put todoo

router.put("/todos/:id",(req,res)=>{
    res.status(200).json({mssg:"PUT REQUEST TO /api/todos/:id"});
});

module.exports =router;

this is part of client folder

import { useEffect } from "react";

 

export default  function App() {

  useEffect(()=> {
      async function getTodos() {
        const res = await fetch("/api/todos");
        const todos = await res.json();

        console.log(todos);
      }
      getTodos();

  },[])


  return (
  <main className="container">

    <h1>The to-do</h1>

  </main>
  ); 
}
 

and we added a proxy in packages.json to bypass the coros policy and shorten the whole http link
to /api/todos to allow it to change the port

any thing more to add

QUESTIONS

1. why am i getting a p token error
   2)if there error is due to lack of fundamental knowledge please enlighten me

i tried the above while following a course on yt.