Connection timed out when remote cluster re-indexing

Elastic Stack Elasticsearch
9

Here is request/response something like

Request :

 curl -X POST "https://vpc-new-cluster-url:443/_reindex?wait_for_completion=false&pretty" -H 'Content-Type: application/json' -d'
{
  "source": {
    "remote": {
      "host": "https://vpc-old-cluster-url:443"
    },
    "index": index0"
  },
  "dest": {
    "index": "index000001"
  }
}
'

Response {
"task" : "taskid2321"
}

Task Details using /_tasks/{taskid}

{
  "completed" : true,
  "task" : {
    "node" : "...",
    "id" : 3232,
    "type" : "transport",
    "action" : "indices:data/write/reindex",
    "status" : {
      "total" : 0,
      "updated" : 0,
      "created" : 0,
      "deleted" : 0,
      "batches" : 0,
      "version_conflicts" : 0,
      "noops" : 0,
      "retries" : {
        "bulk" : 0,
        "search" : 0
      },
      "throttled_millis" : 0,
      "requests_per_second" : -1.0,
      "throttled_until_millis" : 0
    },
    "description" : "...",
    "start_time_in_millis" : 1648449610121,
    "running_time_in_nanos" : 5070569,
    "cancellable" : true,
    "headers" : { }
  },
  "error" : {
    "type" : "null_pointer_exception",
    "reason" : null
  }
}