Fatal error: Uncaught Error: Interface "PayPal\Handler\IPayPalHandler" not found in /var/www/html/ohnishi-test.site/PayPal-PHP-SDK-master/lib/PayPal/Handler/OauthHandler.php:18 Stack trace: #0 {main} thrown in /var/www/html/ohnishi-test.site/PayPal-PHP-SDK-master/lib/PayPal/Handler/OauthHandler.php on line 18