Just in case anyone else is using this very useful setup, to use the JSONRPC method, you need to drop the **condenser_api ** aspect so

curl -s --data '{"jsonrpc":"2.0", "method":"condenser_api.get_discussions_by_created", "params":[{"tag":"steem","limit":1}], "id":1}' https://testnet.steem.vc

becomes

curl -s --data '{"jsonrpc":"2.0", "method":"get_discussions_by_created", "params":[{"tag":"steem","limit":1}], "id":1}' https://testnet.steem.vc