Offline plugin install of Java plugin

I am attempting to install a custom output Logstash plugin on Logstash 7.2; the plugin is written in Java based on the instructions found on this Logstash documentation page.

I am attempting to deploy into a Logstash docker container using the offline plugin install method. When I run the installation, everything appears to be successful:

[root@ca3715a22ecb logstash-core]# logstash-plugin install file:///co360/plugins/co360-plugins.zip
OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.jruby.util.SecurityHelper to field java.lang.reflect.Field.modifiers
WARNING: Please consider reporting this to the maintainers of org.jruby.util.SecurityHelper
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Installing file: /co360/plugins/co360-plugins.zip
Install successful

However, when I start Logstash, I get this error:

[ERROR] 2019-07-26 12:36:36.185 [main] Logstash - java.lang.IllegalStateException: Logstash stopped processing because of an error: (LoadError) Java plugin 'logstash-output-notify_plugin' does not contain a single jar file with the plugin's name and version

In the above error, logstash-output-notify_plugin is the Java plugin I expected to be installed; however, it appears the Jar file can't be reconciled when installing from the offline .zip package. As another point of reference, I installed this same plugin directly from the created gem file and it is able to be used without issue. A few questions:

  1. Is offline installation of Java Logstash plugins supported?
  2. If so, is there something special I need to do to ensure .jar files are included in the offline install package?