How to index Dropbox documents?

Elastic Stack Elasticsearch
2

Sorry, Elastic search version is 7.5.1 in CentOS7.
I went to "/usr/share/elasticsearch" and tried
"$ bin/plugin -install fr.pilato.elasticsearch.river/dropbox/0.1.0"
command which is displaying the below message.

A tool for managing installed elasticsearch plugins

Non-option arguments:
command

Option         Description
------         -----------
-h, --help     show help
-s, --silent   show minimal output
-v, --verbose  show verbose output
ERROR: i is not a recognized option

Am I in the wrong directory or is it a wrong command?

Thanks,
Lisa