Elasticsearch version conflict Issue

[surajdalvi (Suraj)]

I have updated document in the elastic search. after update using, I am fetching the same document by using their ID. It is giving me the following response:

{
"_index": "b123456",
"_type": "documents",
"_id": "bltde56dd11ba998bab",
"_version": 3,
"found": true,
"_source": {
    "title": "index.json",
    "url": "/index1",
    "tags": [],
    "created_at": "2018-06-19T05:02:38.174Z",
    "updated_at": "2018-06-19T05:07:57.155Z",
    "version": 1,
    "fields": [{
            "uid": "fname",
            "value": "john"
        },
        {
            "uid": "lname",
            "value": "test"
        }
    ],
    "class": "first"
}


}

After I am using update_by_query to update document I am sending following request to update_by_query:

{
    "script": {
        "source": "ctx._source.title = params.title;ctx._source.url = params.url;ctx._source.created_at = params.created_at;ctx._source.updated_at = params.updated_at;ctx._source.version = params.version;ctx._source.fields = params.fields",
        "params": {
            "title": "Demo title",
            "url": "/demo",
            "created_at": "2018-06-19T05:02:38.174Z",
            "updated_at": "2018-06-19T05:07:57.155Z",
            "version": 2,
            "fields": [{
                    "uid": "fname",
                    "value": "vicky"
                },
                {
                    "uid": "lname",
                    "value": "test"
                }
            ]
        }
    },
    "query": {
        "bool": {
            "must": [{
                    "term": {
                        "_id": "bltde56dd11ba998bab"
                    }
                },
                {
                    "range": {
                        "version": {
                            "lt": 2
                        }
                    }
                }
            ]
        }
    }
}

But it is giving me status code:409 and following error:

[documents][bltde56dd11ba998bab]: version conflict, current version [3] is different than the one provided [2]

My document also contains custom version key.
Can anyone help me into this?
What is meaning of this error?