For calling SOAP Web services with HTTPS, you need to use the new HTTPClient and upgrade to PB 2019 R2 or newer.  The old SOAP clients in PB do not support TLS 1.2 security.  Many customers are switching over because of this security issue.  This tech article will help guide you how to use the HTTPClient to make SOAP calls: https://community.appeon.com/index.php/articles-blogs/tutorials-articles/2-powerbuilder/236-call-soap-web-services-using-httpclient-object

For calling REST Web APIs with HTTPS, you need to use the new RESTClient and upgrade to PB 2019 R2 or newer.  Before PB 2017, PowerBuilder did not have any REST client built in.  We added this in 2017 and greatly enhanced it in 2019.  This tech article will help guide you about the features of the RESTClient to make REST calls: https://community.appeon.com/index.php/articles-blogs/tutorials-articles/2-powerbuilder/244-rest-enhancements-in-powerbuilder-2019

By the way, I should clarify that for RESTClient it can automatically populate the DataWindow with the JSON data received from the REST Web API.  But for SOAP, you need to parse the XML data and manually populate it into the DataWindow.  So if any chance you can convert the SOAP to REST, that would make your PB coding simpler.