Cannot create Elasticsearch mapping , for Cassandra keyspace

Question

Currently, I am experimenting with Elassandra (combination of Elasticsearch and Cassandra). There I have an existing Cassandra keyspace with tables and want to create a mapping to Elasticsearch so that I can use the Elasticsearch API to search/filter the data.

Unfortunately, it does not work and I am not sure why that is.

First of all, I make a PUT request to the Elasticsearch HTTP endpoint to create the mapping:

PUT company 
{
    "settings": { 
      "keyspace":"ks" 
    },
    "mappings": {
        "t" : {
            "discover":".*"
        }
    }
}

Then I get this as answer:

{
  "error": {
    "root_cause": [
      {
        "type": "illegal_argument_exception",
        "reason": "unknown setting [index.keyspace] please check that any required plugins are installed, or check the breaking changes documentation for removed settings"
      }
    ],
    "type": "illegal_argument_exception",
    "reason": "unknown setting [index.keyspace] please check that any required plugins are installed, or check the breaking changes documentation for removed settings"
  },
  "status": 400
}