how to get json from post response code example

Example: HTTPoison post json

url = "http://myurl"
body = Poison.encode!(%{
  "call": "MyCall",
  "app_key": key,
  "param": [
    %{
      "page": page,
      "registres": registers,
      "filter": filter
    }
  ]
})
headers = [{"Content-type", "application/json"}]
HTTPoison.post(url, body, headers, [])