My apologies, my dummy id and api key were interpreted as html and omitted it seems, they are missing a placeholder.
The URL is meant to be:
http://developer.echonest.com/api/v4/catalog/update?api_key="mykey"&data_type=json&format=json&id="myid"
and the curl:
curl -X POST "http://developer.echonest.com/api/v4/catalog/update" -F "api_key=mykey" -F "data_type=json" -F "format=json" -F "id=myid" -F "data=@jsonSample.json"