Swift POST request to Laravel - Issue with JSON response

Question

I am new to Swift. Trying to make a post request to laravel on localhost. To verify my Request recieved from swift within laravel. I am returning Request as JSON response. which produces this error.

Code 3840 "JSON text did not start with array or object and option to allow fragments not set."

Which means a malformed JSON response.

Laravel UserController

public function verify_login(Request $request)
{
  return response()->json($request)
}

ViewController.swift

 @IBAction func verify_login(_ sender: UIButton) {
    let username: String = self.username.text!
    let passkey: String = self.passkey.text!
    //print(username)
    let urlString = "http://localhost:8888/user/verify"

    guard let requestUrl = URL(string:urlString) else { return }

    let parameters = "username=\(username)&passkey=\(passkey)"
    var request = URLRequest(url:requestUrl)
    request.httpMethod = "POST"
    request.setValue("application/x-www-form-unlencoded;charset=utf-8", forHTTPHeaderField: "Content-Type")
    request.httpBody = parameters.data(using: String.Encoding.utf8)

    let task = URLSession.shared.dataTask(with: request) {
        (data, response, error) in
        if error == nil,let usableData = data {
            var json: [String: Any]?
            do {
                json = try JSONSerialization.jsonObject(with: usableData) as? [String:Any]
                print(json?["username"]! as Any)

            }catch{
                print(error)
            }
        }
    }

    task.resume()
    }

NOTE:

1. Using Postman I recieve the expected response (Request object as json).
2. Swift end code works fine with JSON Placeholder API