In case it is in XML format, so we just pass the XML request to the Transact API URL by using php-curl with text/xml as the request header/content-type. But, if it uses Form Fields, then we should construct a new XML content and then pass tp Transact API URL using curl.
So, there should be a content-type checking on each request in order we could differentiate the process. But, the end process would be the same, using php-curl with text/xml as the content-typ.e