How to query on computed script_fields?

Elastic Stack Elasticsearch
1

Hello, I would like to query on a script field.
I'm trying this query without success :

{
  "query": {
    "multi_match": {
      "query": "machinbidule",
      "fields": [
        "name^9",
        "concatenated_synonyms^8",
        "x_long_description^7",
        "code_prefix^6",
        "x_colors^5"
      ],
      "type": "best_fields",
      "tie_breaker": 0.3,
      "fuzziness": 2
    }
  },
  "script_fields": {
    "concatenated_synonyms": {
      "script": {
        "lang": "painless",
        "source": "String.join(',', params._source.x_synonyms.stream().map(s -> s.name).collect(Collectors.toList()))"
      }
    }
  }
}

Could you help me to fix this query ?

Thank you,

best regards,

Nicolas