@timestamp missing exception for datastream

[Sankar_S]

Getting the below exception while indexing the document into datastream

org.elasticsearch.ElasticsearchException: Elasticsearch exception [type=illegal_argument_exception, reason=data stream timestamp field [@timestamp] is missing]

Injest Pipeline
PUT _ingest/pipeline/auto_now_add
{
"description": "Assigns the current date if not yet present and if the index name is whitelisted",
"processors": [
{
"script": {
"source": """
// skip if not whitelisted
if (![ "cp_monitoring_data_tenantid"
].contains(ctx['_index'])) { return; }

       // always update updated_at
      ctx['@timestamp'] = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ").format(new Date());
      // don't overwrite if present
      if (ctx != null && ctx['created_at'] != null) { return; }
      
      ctx['created_at'] = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ").format(new Date());
    """
  }
}

]
}

Model Object
public class Message {
@Id
private String id;

public Date getDate() {
    return date;
}

public void setDate(Date date) {
    this.date = date;
}

@Field(type= FieldType.Date)
Date date;

@Field(type = FieldType.Keyword)
private String message;

@Field(type= FieldType.Date)
private Date timestamp;

public String getId() {
    return id;
}

public void setId(String id) {
    this.id = id;
}

public String getMessage() {
    return message;
}

public void setMessage(String message) {
    this.message = message;
}

Mappings

<code>{
  "dynamic": true,
  "properties": {
    "date": {
      "format": "strict_date_time",
      "type": "date"
    },
    "index_age": {
      "type": "long"
    },
    "@timestamp": {
      "format": "yyyy-MM-dd'T'HH:mm:ss.SSSZ",
      "type": "date"
    },
    "timestamp": {
      "format": "yyyy-MM-dd'T'HH:mm:ss.SSSZ",
      "type": "date"
    }
  }
}
</>
Please let me know why is it failing how to fix it.