Hi Michael!
Is your intention to send and receive plain JSON data? As in, a JSON object you define yourself?
In that case, you should use HttpClient which is more suited for this use case. You can find some usage examples in our documentation here
RestClient is more oriented towards sending and retrieving Data Window objects from a REST API. If that's what you're trying to do, we also have documentation that demonstrates these use cases: here and here
Hope this helps.
Regards,
Francisco