Help with using dynamic template

I get the following error when using dynamic_templates, I'd like to map the fields with k8s.* as text and nested object field "network" as a flat_object.
I've tried using both regex and path_match but get the same error.

Can anyone let me know if I'm doing it correctly?

Configuration:

PUT _index_template/test_logs
{
  "index_patterns": [
    "test_*"
  ],
  "template": {
    "mappings": {
      "dynamic_templates": [
        {
          "k8s_fields_as_text": {
            "match_pattern": "regex",
            "match": "^k8s.*",
            "mapping": {
              "type": "text"
            }
          }
        },
        {
          "nested_object_fields_as_flat_object": {
            "match": "*",
            "match_mapping_type": "object",
            "mapping": {
              "type": "flat_object"
            }
          }
        }        
      ]   
    }
  }
}
PUT test_logs/_doc/1
{
  "k8s.application.name": "test-app",
  "k8s.container.restart_count": "0",  
  "k8s.namespace.name": "test",
  "k8s.pod.name": "test-app-9f45bf4b-v76fr",
  "network": {
    "ip_address": "10.10.1.15", 
    "security_group_id": "sg-111111111111111", 
    "subnet_id": "subnet-111111111111111",
    "vpc_id": "vpc-111111111111111"
  }
}

Error:

{
  "error": {
    "root_cause": [
      {
        "type": "class_cast_exception",
        "reason": "class_cast_exception: class org.opensearch.index.mapper.TextFieldMapper cannot be cast to class org.opensearch.index.mapper.ObjectMapper (org.opensearch.index.mapper.TextFieldMapper and org.opensearch.index.mapper.ObjectMapper are in unnamed module of loader 'app')"
      }
    ],
    "type": "mapper_parsing_exception",
    "reason": "failed to parse",
    "caused_by": {
      "type": "class_cast_exception",
      "reason": "class_cast_exception: class org.opensearch.index.mapper.TextFieldMapper cannot be cast to class org.opensearch.index.mapper.ObjectMapper (org.opensearch.index.mapper.TextFieldMapper and org.opensearch.index.mapper.ObjectMapper are in unnamed module of loader 'app')"
    }
  },
  "status": 400
}

Note: I'm using OpenSearch 2.11 and they don't have documentation on dynamic_templates hence I've raised a topic here.

OpenSearch/OpenDistro are AWS run products and differ from the original Elasticsearch and Kibana products that Elastic builds and maintains. You may need to contact them directly for further assistance.

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Opensearch is not supported here, you will need to direct this question to an Opensearch forum.