not-found page of NextJS is automatically refreshing the website

Question

My NextJS App is refreshing again and again by itself when I am hitting a route that is not defined.

Here is my folder structure.

App
 - Home
    page.js
 - Service
    page.js
 page.js
 not-found.js

The not-found.js is below:

const NotFoundPage = () => {
  return (
    <div>
      <p>Sorry this page doesn't exist</p>
    </div>
  );
};
export default NotFoundPage;

version:

"next": "13.4.5",
"react": "18.2.0",