How to provide an object from third party components to TestExecute REST API?

Hello.

I'm trying to communicate with TestExecute REST API.
When executing GET/POST requests with parameters simple data types everything is Ok.
But there are some methods from third party components that are expecting an object from some their class.
How to obtain this?
object.SomeMethod(someObject)
I have id - identification for object whoes method is trying to be executed and
someObject is object from third party components, which identifications also is available.

From Visual Studio 2017, C#.

Thanks in advance,
Maria