paulftw commented :
This is happening because query doesn’t parse as JSON so it’s sent as RDF.
If Ratel sent it as JSON there’d be a different though more relevant syntax error returned.
Correct JSON:
{"set":[{"uid":"_:root","connects":[{"name": "A"},{"name":"B"}]}]}
Incorrect JSON:
{"set":[{"uid":"_:root","connects":[{"name": "A"},{"name":"B"}]]}
Note one more curly closing bracket in the end of the correct query.
I’m closing this issue as working as expected and will file a feature request to provide a visual indication of the detected content-type.