Fatal error: Uncaught Error: Class 'Nexmo\Client\Callback\Callback' not found in /home/flexinettek/public_html/vendor/nexmo/client/src/Message/Callback/Receipt.php:12 Stack trace: #0 {main} thrown in /home/flexinettek/public_html/vendor/nexmo/client/src/Message/Callback/Receipt.php on line 12