When using this package with other API packages, such as ebay-sdk, php blocks each curl process until the previous one is completed. Curl multi-request allows php to simultaneously make multiple API requests without blocking.
To utilize this feature, the ability to return just the request string alone was needed.
$queryString = $apaiIO->getRequestString($search);
Read more about Apai-IO here:
https://github.com/exeu/apai-io