Laravel API routes not working with Postman

My route/api.php has these routes:

Route::post('/signup' , 'UserApiController@signup');
Route::post('/logout' , 'UserApiController@logout');
Route::post('/verify' , 'UserApiController@verify');

but when I’m trying to access from Postman like this, it shows object not found:

localhost/my_webiste/api/signup

here the userapicontroller signup function:

public function signup(Request $request)
{
    $this->validate($request, [
            'social_unique_id' => ['required_if:login_by,facebook,google','unique:users'],
            'device_type' => 'required|in:android,ios',
            'device_token' => 'required',
            'device_id' => 'required',
            'login_by' => 'required|in:manual,facebook,google',
            'first_name' => 'required|max:255',
            'last_name' => 'required|max:255',
            'email' => 'required|email|max:255|unique:users',
            'mobile' => 'required',
            'password' => 'required|min:6',
        ]);

    try{

        $User = $request->all();

        $User['payment_mode'] = 'CASH';
        $User['password'] = bcrypt($request->password);
        $User = User::create($User);

        return $User;
    } catch (Exception $e) {
         return response()->json(['error' => trans('api.something_went_wrong')], 500);
    }
}

here the postman output of post request of localhost/mywebsite/api/signup :

    <title>Object not found!</title>
    <link rev="made" href="mailto:postmaster@localhost" />
   <h1>Object not found!</h1>
   The requested URL was not found on this server.
   If you entered the URL manually please check your
spelling and try again.