I'm making an dependent drop-down of countries states and cities in Laravel 9 using jQuery and Ajax but getting an 500 internal server

I'm making an dependent drop-downn of countries states and cities in laravel using jQuery and Ajax. I'm doing it on localhost Xampp. First i use jQuery for country. when country change jQuery get value and send to Controller. But when i send value from RegistrationFormComponent to CountryStateCity Controller and try to show what value i get. I got an error ( POST http://127.0.0.1:8000/getstate 500 (Internal Server Error) ). i don't know why im getting this error.

Route:

Route::get('/register', [CountryStateCityController::class, 'getcountry']);
Route::POST('/getstate ', [CountryStateCityController::class, 'getstate']);

JQuery and Ajax

$.ajaxSetup({
    headers: {
        'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
    }
});

$(document).ready(function () {
  $('#country').change(function () {
    var cid = this.value;   //$(this).val(); we cal also write this.
    $.ajax({
      url: "getstate",
      type: "POST",
      datatype: "json",
      data: {
        country_id: cid,
      },
      success: function(result) {
        // if(cid == "success")
        //   alert(response);
          console.log(result);
      },
      errror: function(xhr) {
          console.log(xhr.responseText);
        }
      });
  });
});

Controller

class CountryStateCityController extends Controller
{
    public function getcountry() {
        $country = DB::table('countries')->get();
        $data = compact('country');
        return view('RegistrationForm')->with($data);
    }

    public function getstate(Request $request) {
        
        $state = State::where('countryid'->$cid)->get();
        return response()->json($state);
    }

    public function getcity() {
    }
}

I think i tryed every possible thing. But didn't work. Please tell me how can i get rid of this problem. And please also tell me how can i send data from component to controller using jquery and ajax and get value form controller and take data from database and send back to component.

This is written incorrectly.

public function getstate(Request $request) {
        
        $state = State::where('countryid'->$cid)->get();
        return response()->json($state);
    }

It should look like this.

public function getstate(Request $request) {
        
        $state = State::where('countryid', '=', $request->country_id)->get();
        return response()->json($state);
    }