使用Ajax在Joomla的类中自动加载一个类

Question

I'm writing a Joomla module.

As part of this I'm using an ajax call (using 3.x)

the ajax etc works fine. However I want to use an object autoloader within the ajax class but I can't figure out what I'm doing wrong (it works fine as standalone code just breaks implementing with Joomla and ajax)

I have this for the Joomla class:

    public function getAjax()
        {
            $input = JFactory::getApplication()->input;
            $cmd  = $input->get('cmd');

            if($cmd =="setPayment"){
             require  __DIR__ . '/PayPal-PHP-SDK/autoload.php';
             use PayPal\Api\Amount;     
             use PayPal\Api\Details;

The code cannot find the Amount and Details classes. I'm assuming that it's to do with the context I'm calling them.

Can someone help?