Kibana/Elasticsearch 6.8 - delete_by_query returns reason "blocked by: [FORBIDDEN/8/index write (api)];"

I'm using the Dev Tools in Kibana 6.8 to delete docs by query but I received a 403 with the type "cluster_block_exception", reason "blocked by: [FORBIDDEN/8/index write (api)];".

I used the following command:

curl -XPOST "http://localhost:9200/my_index/_delete_by_query" -H 'Content-Type: application/json' -d'
{
  "query": {
    "match_all": {}
  }
}'

Here's a sample response:

{
  "took": 26,
  "timed_out": false,
  "total": 2,
  "deleted": 0,
  "batches": 1,
  "version_conflicts": 0,
  "noops": 0,
  "retries": {
    "bulk": 0,
    "search": 0
  },
  "throttled_millis": 0,
  "requests_per_second": -1,
  "throttled_until_millis": 0,
  "failures": [
    {
      "index": "my_index",
      "type": "doc",
      "id": "TnOKCHMBlyetxY-P6HZ_",
      "cause": {
        "type": "cluster_block_exception",
        "reason": "blocked by: [FORBIDDEN/8/index write (api)];"
      },
      "status": 403
    },
    {
      "index": "my_index",
      "type": "doc",
      "id": "T3OKCHMBlyetxY-P6XYF",
      "cause": {
        "type": "cluster_block_exception",
        "reason": "blocked by: [FORBIDDEN/8/index write (api)];"
      },
      "status": 403
    }
  ]
}

Any help on how to set the proper permissions would be greatly appreciated. Thanks.

You could try to first change the state of the index with this request :

PUT /my_index/_settings { "index": { "blocks": { "write": "false" } } }

And in second time, you have to identify which cause this state of index (indices policy, FileSystem : "low watermark" of 85%?)