This feature is currently available to Enterprise level customers. We’re working on a feature to allow an API for data retrieval to other tiers.
Currently, the APIs available via groker.initialstate.com accept GET and POST verbs both for submitting data (because of a previous request from users who didn't have the ability to change the verb to POST, so GET is accepted as a POST).
There is currently a separate API for retrieving data for Enterprise customers. And there is an entirely new API that is in development that is planned to be released to other paid tiers for retrieving data via API.
In the mean time. Data is available for CSV download for EVERY tier within the Source app at app.initialstate.com
This functionality is possible, but not yet exposed to the UI yet.