Cannot use body and headers with GET method, Solution 1 - Instead of GET method you can make the method as POST or PUT to send body and headers.

Solution 2 - If you want to send data with GET method you can send it as queryParams

const userDetails = { name: "john", email: "[email protected]", password: "1234", }

    const queryParams = new URLSearchParams(userDetails).toString();

You can send queryParams in api url as

await fetch(`http://localhost:8001/user?${queryParams}`, {
      method: "GET",
    });

and receive it as req.query in backend