Elasticsearch date mapping parsing failures

Question

I have documents with timestamps.

"features.timestamp" : "1631113703.342163".

When I'm trying to map it to "date" type

{
  "mappings": {
    "numeric_detection": true,
    "dynamic_templates": [
      {
        "strings_as_keywords": {
          "match_mapping_type": "string",
          "mapping": {
            "norms": false,
            "type": "keyword"
          }
        }
      }
    ],
    "properties": {
      "features.timestamp":{
        "type": "date"
      }
    }
  }
}

, error occures:

"failed to parse field [features.timestamp] of type [date] in document with id '0PTzxXsBtw6JSLuk-bPF'. Preview of field's value: '1631113703.342163'"

How to process these timestamp into nice @timestamp property?