By the way, when the request body is malformed it seems the response body returned is always text/plain regardless of the accept header

{:status 400, :headers {"content-length" "62", "content-type" "text/plain;charset=utf-8"}, :body "Malformed body\r\n\r\n{:status 400, :error {:bar disallowed-key}}\n"}

Another possible issue: an invalid accept header like this:

"application/transit+json;, application/json;q=0.6"