Elasticsearch : Root mapping definition has unsupported parameters index : not_analyzed

Hi all I am trying to create schema Test.

PUT /test
{
    "mappings": {
        "field1": {
            "type": "integer"
        },
        "field2": {  
            "type": "integer"
        },
        "field3": {
            "type": "string",
            "index": "not_analyzed"
        },
        "field4": {
            "type": "string",
            "analyzer": "autocomplete",
            "search_analyzer": "standard"
        }
    },
    "settings": {
        bla
        bla
        bla
    }
}

I am getting the following error

{
    "error": {
        "root_cause": [{
            "type": "mapper_parsing_exception",
            "reason": "Root mapping definition has unsupported parameters: [index : not_analyzed] [type : string]"
        }],
        "type": "mapper_parsing_exception",
        "reason": "Failed to parse mapping [featured]: Root mapping definition has unsupported parameters:  [index : not_analyzed] [type : string]",
        "caused_by": {
            "type": "mapper_parsing_exception",
            "reason": "Root mapping definition has unsupported parameters:  [index : not_analyzed] [type : string]"
        }
    },
    "status": 400
}

Please help me to resolve this error