Fatal error: Uncaught Error: Class 'Nexmo\Client\Callback\Callback' not found in /opt/lampp/htdocs/kuesioner/vendor/nexmo/client-core/src/Message/Callback/Receipt.php:12 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/kuesioner/vendor/nexmo/client-core/src/Message/Callback/Receipt.php on line 12