While we use this webservide, they providing some functions. each functions requesting to provide some argument values. How can work with httpclient method ?

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While we call werservice they providing some functions. 

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while use datawindow - webservice(source) - giving arguments.. while retrieve getting message. this in 2019R3

Thanks to all

There's a little more coding involved when using the HTTPClient, but you will have access to all the same methods.  In this case, your best bet is to use a tool like Postman (or SoapUI).  First consume the WSDL with one of the tools I mentioned, then get each call working in Postman/SoapUI.  Once it's working, you can see exactly what the HTTP request and response look like, and you can duplicate that with the HTTPClient.  Many web service providers still offer their services in SOAP but will often provide those same services in REST as well.  Might want to check with the service provider if you find REST easier to work with.  Either way, you will be able to consume from PB2019 R3.

Actually there are only one webservice link. 

I used this link in pb12 in the proxy-soap method and work it perfectly. But, webservice team changed the protocol into tls1.2. so, pb12 not supporting that protocol. So, result getting blank and throwing errors.

In pb12, while we deploy the proxy, it will generate a structure. in this structure they are providing no of functions. To that functions we need to apply some username, password....etc. But, my doubt is while we use httpclient method will get there all functions ?

What do you want to know about it?  You can call both SOAP and REST webservices using PB2017 or PB2019.  You will want to look at objects like the HTTPClient, RESTClient, OAuthClient, JSONParser, JSONPackage and JSONGenerator  depending what type of web service you want to call.  This may help you get started:

https://docs.appeon.com/pb2017r2/whats_new/ch01s01.html

https://www.youtube.com/watch?v=_sMpCIOZap0

If you have any specific questions, let us know.