Что-то пошло не так

Deprecated: Non-static method App\KPS::isAdmin() should not be called statically in /var/www/k-ps.ru/agg/index.php on line 20

Fatal error: Uncaught Error: Using $this when not in object context in /var/www/k-ps.ru/agg/classes/App/KPS.php:23 Stack trace: #0 /var/www/k-ps.ru/agg/index.php(20): App\KPS::isAdmin() #1 {main} thrown in /var/www/k-ps.ru/agg/classes/App/KPS.php on line 23