I am trying to use Solr's
Unknown top-level key in JSON request : group...
What I am looking for is the
JSON Request API. Unfortunately, it seems that it is discontinued. In October 2016 Yonik wrote: "The JSON Request API is currently in it’s infancy – only a few query parameters are supported". The latest official documentation about the API is from 2015: https://cwiki.apache.org/confluence/display/solr/JSON+Request+API (and was also created by someone called Yonik. Coincidence?!) But it is not mentioned in the current reference guides Apache Solr 6.5/6.6.
So the answer is: Result grouping cannot be accessed via a JSON query. Note: Same is true for the more current Collapse and Expand components.