laravel 8, Class "App\Http\Controllers\Admin\Category" not found {"exception":{}}

I am studying Laravel 8, using this code, but error :( please tell me how to fix

Class "App\Http\Controllers\Admin\Category" not found {"exception":{}}

code in Category Controller.php

namespace App\Http\Controllers\Admin;

use App\Http\Controllers\Controller;
use Illuminate\Http\Request;

class CategoryController extends Controller
{
        public function index()
    {
      $categories = Category::paginate(2);
        return view('admin.categories.index', compact('categories'));
    }

code in web.php

use Illuminate\Support\Facades\Route;
Route::get('/', function() {
    return view('welcome');
});

Route::group(['prefix' => 'admin', 'namespace' => 'Admin'], function () {
        Route::get('/', 'MainController@index')->name('admin.index');
        Route::resource('/categories', 'CategoryController');
});

source https://stackoverflow.com/questions/68145482/laravel-8-class-app-http-controllers-admin-category-not-found-exception