Indices names missing timestamp

elasticsearch index name is not created correctly, here is the logstash config:

output {
  #stdout { codec => rubydebug }
  elasticsearch {
     hosts => "es.example.com:443"
     ssl => true
     ssl_certificate_verification => true
     user => xxxxxxxx
     password => yyyyyyyyy
     manage_template => false
     index => "klogs-%{+YYYY.MM.dd}"
  }
}

index is missing "%{+YYYY.MM.dd}", what can be wrong here? logstash version is 7.1.1 and ES version 7.4.1

I moved this post to the Logstash forum.

That would happen if you have deleted the @timestamp field -- the sprintf reference to @timestamp will produce an empty string.

i was removing @timestamp field, it creates the index correctly after keeping @timestamp field.