Great news!
I thought this extension was only for cases where the call was with XML/SOAP, but in my case, it's JSON/REST. However, using it this way, the properties appear as I wanted them to. Thank you very much for your help!

Thank you for the comment, Michael! Even though all the properties are filled, I did it the way you mentioned, but it still didn't work. I also tried adding an initial expression, but the content still appears empty. The solution was to set the extended request class as %XML.Adaptor, but either way, I appreciate your help.