Json parameters of Unity Http Post request

Using Litjson

    void Start () 
    { 
        // Use litJson to create parameter data in json format 
        JsonData data = new JsonData (); 
        data [ " Parameter name negotiated with backend " ] = " Parameter you want to write " ;
         byte [] postBytes = System.Text.Encoding.Default.GetBytes (data.ToJson ()); 

        // use native UnityWebRequest (recommended) 
        StartCoroutine (UnityWebRequestPost ( " your url " , postBytes)); 

        // use UniRx 
        ObservableWWW.Post ( " you Url " , postBytes, new Dictionary < string, string>() { { "Content-Type", "application/json" } })
                     .Subscribe(result => Debug.Log(result));
    }

    IEnumerator UnityWebRequestPost(string url, byte[] postBytes)
    {
        UnityWebRequest request = new UnityWebRequest(url, "POST");

        request.uploadHandler = (UploadHandler)new UploadHandlerRaw(postBytes);
        request.downloadHandler = (DownloadHandler)new DownloadHandlerBuffer();
        request.SetRequestHeader("Content-Type", "application/json");
        yield return request.SendWebRequest();
        Debug.Log("Status Code: " + request.responseCode);
        if (request.isNetworkError || request.isHttpError)
        {
            Debug.LogError(request.error);
        }
        else
        {
            Debug.Log(request.downloadHandler.text);
        }
    }