Dynamic mapping strict to true

Elastic Stack Elasticsearch
5

Sorry I might not have explain properly
I am talking about creating template

Here is exactly what happens. using your example. it must be some bug or I am doing something wrong

Works - Created template

PUT _index_template/test
{
  "index_patterns": ["test*"],
  "template": {
    "settings": {
      "number_of_shards": 1,
      "number_of_replicas": "1"
    },
  "mappings": {
    "dynamic": "strict",
    "properties": {
      "@timestamp": {
        "type": "date"
      },
      "number": {
        "type": "long"
      },
      "word": {
        "type": "keyword"
      }
    }
  }
}
}

Works - Put one record to index

POST test/_doc/1
{
  "number": 5,
  "word": "test"
}

Failed as it suppose to fail, because I don't have extrafield define.
works as expected

POST test/_doc/1
{
  "number": 5,
  "word": "test",
  "extrafield": "yes"
}

Now change template to dynamic=true, and added new field called extrafield

PUT _index_template/test
{
  "index_patterns": ["test*"],
  "template": {
    "settings": {
      "number_of_shards": 1,
      "number_of_replicas": "1"
    },
  "mappings": {
    "dynamic": "true",
    "properties": {
      "@timestamp": {
        "type": "date"
      },
      "number": {
        "type": "long"
      },
      "word": {
        "type": "keyword"
      },
      **"extrafield"**:{
        "type": "boolean"
      }
    }
  }
}
}

This should work Right? because I have extrafield define and mapping dynamic = true but it fails

POST test/_doc/1
{
  "number": 5,
  "word": "test",
  "extrafield": "yes"
}

ERROR, Even though dynamic=true.

GET _index_template/test  --> this tells me dynamic=true

{
  "error" : {
    "root_cause" : [
      {
        "type" : "strict_dynamic_mapping_exception",
        "reason" : "mapping set to strict, dynamic introduction of [extrafield] within [_doc] is not allowed"
      }
    ],
    "type" : "strict_dynamic_mapping_exception",
    "reason" : "mapping set to strict, dynamic introduction of [extrafield] within [_doc] is not allowed"
  },
  "status" : 400
}