Class 'Carbon\\Carbon' not found

[liwong2023]

Hi! friend, why my code have error after the code start? It show that: PHP Fatal error: Uncaught Error: Class 'Carbon\Carbon' not found, and my code is:
require_once $_SERVER['DOCUMENT_ROOT'] . '/vendor/autoload.php';
use Carbon\Carbon;
use Chanthorn\CarbonKh\ToKhmerDate;
$date = Carbon::parse(strtotime($dateofWeek));
$khmerLunarDate = new ToKhmerDate($date);
echo $khmerLunarDate::format();
Thanks