Fluentd not able to find fluent-plugin-mongo as input plugin

[vidhi1233]

fluent-plugin-mongo is installed corrected as shown:
sudo /opt/td-agent/bin/fluent-gem list | grep "fluent-plugin-mongo"
fluent-plugin-mongo (1.6.0)

still getting error:
[error]: config error file="/etc/td-agent/td-agent.conf" error_class=Fluent::NotFoundPluginError error="Unknown input plugin 'mongo'.

conf file in: /etc/td-agent/td-agent.conf as below:

<source>
  @type mongo
  host "host"
  port "port"
  database "db"
  collection "collection"
  tag mongo_logs
</source>