Actually I can't use "Step Into" debug if a server action doesn't belong to the actual eSpace, even this isn't a System eSpace.
Example, I have a "REST Integration Core" for Google API's eSpace and an another Google People API to consume these specific methods. While debugging, step into a REST Integration Core action, the Service Studio doesn't open to detailed debug, an option is creating a single WebScreen with only one button points to an action with desired params.