es dynamic templates

mytemplate.json

{
    "mytemplate": {
        "mappings": {
            "_default_": {
                "_all": {
                    "enabled": false
                },
                "_ttl": {
                    "default": "1d",
                    "enabled": true
                },
                "dynamic_templates": [
                    {
                        "int_template": {
                            "match_mapping_type": "long",
                            "mapping": {
                                "type": "integer"
                            },
                            "match": "*"
                        },
                        "float_template": {
                            "match_mapping_type": "double",
                            "mapping": {
                                "type": "float"
                            },
                            "match": "*"
                        },
                        "string_template": {
                            "match_mapping_type": "string",
                            "mapping": {
                                "index": "not_analyzed",
                                "type": "string"
                            },
                            "match": "*"
                        }
                    }
                ],
                "_source": {
                    "enabled": true
                }
            }
        }
    }
}

What is wrong with this template?

[indices/create]]; nested: MapperParsingException[mapping [_default_]]; nested: MapperParsingException[A dynamic template must be defined with a name]; ","status":400}