Logstash dateparsefailure

[Orest_Gulman]

Hi.
My log timestamp has a format Sep 2, 2020 @ 11:14:00.000
When I'm trying to parse it in logstash config I'm getting an error _dateparsefailure

   date {
       target => "@timestamp"
       match => [ "timestamp", "MMM dd, yyyy @ hh:mm:ss.SSS" ]
    }

I can configure the index pattern in Kibana to use timestamp as the timestamp field, but it would be great if someone explains what I'm going wrong.
Thanks.

[Orest_Gulman]

stdout { codec => rubydebug } shows "timestamp" => "2020-09-02T09:13:00.000Z",
I solve it by firstly converting timestamp to string and then parse it using ISO8601 pattern.

    mutate {
      convert => {"timestamp" => "string"}
    }
    date {
      match => ["timestamp", "ISO8601"]
    }