Elastic - Nested Mapping ReIndex

Question

I created an elastic document with dynamic mapping. As by default elastic does not take the json array as nested but i wanted the mapping to be nested. As a solution i had to create a new index with mapping changes to nested and reindex all the data.

I did that but while trying to reindex data elastic is giving illegal argument exception. ( object mapping [performedActions] can't be changed from nested to non-nested)

My Earlier Index -    `"performedActions" : {
            "properties" : {
              "actionTs" : {
                "type" : "text",
                "fields" : {
                  "keyword" : {
                    "type" : "keyword",
                    "ignore_above" : 256
                  }
                }
              },`






New One -  ` "performedActions" : {
            "type" : "nested",
            "properties" : {
              "actionTs" : {
                "type" : "text",
                "fields" : {
                  "keyword" : {
                    "type" : "keyword",
                    "ignore_above" : 256
                  }
                }
`

Reindex CURL 

     curl -XPOST 'localhost:9200/_reindex?pretty' -H 'Content-Type: application/json' -d'
{
  "source": {
    "index": "pendingonme"
  },
  "dest": {
    "index": "action"
  }
}