So I am trying to integrate authorize.net with PHP and I am getting this errors

Warning: include(C:\xampp\htdocs\authorize-net/vendor/jms/serializer/src/JMS/Serializer/Annotation/Type.php): failed to open stream: No such file or directory in C:\xampp\htdocs\authorize-net\autoload.php on line 16

Warning: include(): Failed opening 'C:\xampp\htdocs\authorize-net/vendor/jms/serializer/src/JMS/Serializer/Annotation/Type.php' for inclusion (include_path='.;C:\xampp\php\PEAR') in C:\xampp\htdocs\authorize-net\autoload.php on line 16

Fatal error: Class 'JMS\Serializer\Annotation\Type' not found in C:\xampp\htdocs\authorize-net\lib\net\authorize\util\SensitiveDataConfigType.php on line 6

I downloaded the zipfile from github to get started ... https://github.com/AuthorizeNet/sdk-php

what's causing this error ?