Help with installing 3rd party plugin

I am trying to install the logtash-okta-input plugin. I believe I have built the jruby gem correctly. I build it on a separate machine which matched the Java ver as the server where this will run. I am trying to install the plugin and I get an error.

"ERROR: Could not find a valid gem 'manticore' (>= 0.5.2, < 1.0.0) (required by 'logstash-mixin-http_client-7.0.0.gem'cd /usr/share/logstash' "
when I "list gems" a version of manticore which is within that range is shown. I think what I need to do is to list this manticore path in the Gemfile within logstash where the "install" command is being launched.
When I open the Gemfile to edit it says at the top that I should not manually edit this file. How do I edit this file? What file do I edit and then how is this file generated?
As ussual
Thank you for any assistance.