'Invalid watch actions' when saving/creating a watcher that simulates correctly

[Rom1]

Dear all,

I created a watcher through the Kibana UI that search for documents and index results into a new index.
It works fine when I simulate it, even with execution of actions (target index is populated)

But

• when I want to create it (by pushing the 'create watch' button) I have the message 'invalid watch actions'
• Then I created it with a query 'PUT _watcher/watch/...' successfully but when I look at the watchers through Kibana (Management/Watcher) the state is 'Config error' with the same message when I focus on my watcher.
• The action 'index_evt_type' contains errors 'JSON argument must contain an actionJson.index.index property'

{
  "trigger": {
    "schedule": {
      "interval": "12h"
    }
  },
  "input": {
    "search": {
      "request": {
        "search_type": "query_then_fetch",
        "indices": [
          "index-data"
        ],
        "rest_total_hits_as_int": true,
        "body": {
          "size": 0,
          "query": {
            "bool": {
              "filter": [
                {
                  "range": {
                    "@timestamp": {
                      "gte": "now-1h",
                      "lte": "now"
                    }
                  }
                },
                {
                  "match_all": {}
                }
              ]
            }
          },
          "aggs": {
            "evt_type": {
              "terms": {
                "field": "evt.type",
                "size": 100
              }
            }
          }
        }
      }
    }
  },
  "condition": {
    "always": {}
  },
  "actions": {
    "index_evt_type": {
      "transform": {
        "script": {
          "source": "def documents = ctx.payload.aggregations.evt_type.buckets.stream().map(bucket -> [ '_index': 'index-liste', '_id': 'evt.type.' + bucket.key, 'evt.type': bucket.key, 'tech.data.type': 'evt.type']).collect(Collectors.toList());return [ '_doc' : documents];",
          "lang": "painless"
        }
      },
      "index": {}
    }
  }
}

Does someone have any idea of what's happening ?

[Rom1]

Found it:
"index": { "index": "index-liste" }