How to send elasticsearch multi search request in Postman?

I'm trying to send elasticserach multi search request via postman as below:

POST - http://localhost:9200/_msearch
content-type : x-www-form-urlencoded
body:
{"index":"accounts"}
{"query":{"bool":{"should":[{"match":{"owner.first_name":"Creeple"}}]}}}

However, I'm getting following error:

{
  "error": {
    "root_cause": [
      {
        "type": "parse_exception",
        "reason": "Failed to derive xcontent"
      }
    ],
    "type": "parse_exception",
    "reason": "Failed to derive xcontent"
  },
  "status": 400
}

Note that if I perform same request via my play code, results are succesfully fetched.

WS.url("localhost:9200/_msearch").withHeaders("Content-type" -> "application/x-www-form-urlencoded").post(query)