Filebeat doesn't send any logs to logstash

Elastic Stack Beats
4

We are using filebeat-6.3.1. I don't see any error message on logstash even with debug mode enabled.

output {
   amazon_es {
       hosts  => ["<aws-es>"]
       region => "<aws-region>"
       index  => "flow-logs-%{+YYYY.MM.dd}"
       codec => "json"
   }
   stdout {
      debug => true
   }
}