Hi Eya,
If it's a REST service, why do you use a JSON Deserialize? You should use the native OutSystems Platform REST capabilities to convert the content that is sent to Structures, wherever possible.
If you are talking specifically about the "content" part, if that's actual JSON (rather than a string of escaped JSON), you'll need to add that to the structures you use in the REST consume. Alternatively, but this is not adviced if there's not a specific good need, you could use the On After Response to deserialize things.