Enabling Curl support is one of the prerequisites to start with PHP integration. To know if Curl is supported by your server, Run phpinfo() from your production server and this lists the complete information about your server. You will be able to find if curl is supported by your server or not.

If your servers does not provide curl support, we recommend you to do the integration in sync mode by altering the _async_http_post in the ss2_config file to false.