Reactjs – Getting Error 404 when calling a Api router in Nextjs 14

I searched in articles and YouTube videos about how to fix error 404 when calling a API router for example /api/hello/

even when I saw the documentation in Next.js website I didn’t find any solution for this problem, and I even create a new project from scratch, but the solution is still exist.

this is the simple API router code of app/api/hello/router.ts

import { NextResponse, NextRequest } from "next/server";

export async function GET(request: NextRequest) {
  return NextResponse.json({
    messsage: "hello world",
  });
}

I really need a help form this error