I have been using the following code for the elasticsearch output plugin of a logstash, but it creates the index named as mt-raw-00001

        output {
          elasticsearch {
            hosts => [ "${ECK_ES_HOSTS}" ]
            user => "${ECK_ES_USER}"
            password => "${ECK_ES_PASSWORD}"
            ssl_certificate_authorities => "${ECK_ES_SSL_CERTIFICATE_AUTHORITY}"
            index => "mt-raw-%{+YYYY.MM.dd}"
            # index => "mt-raw"
            data_stream => false
            ilm_enabled => "true"
            ilm_pattern => "00001"
            ilm_rollover_alias => "mt-raw"
            ilm_policy => "mt-ilm"
            manage_template => "true"
            template_name => "mt"
          }

I tried with
index => "mt-raw-%{+YYYY.MM.dd}"
and
index => "mt-raw-%{+yyyy.MM.dd}"
but the result is the same.

How can I resolve this issue?