Now

After install the statistics-gatherer-plugin (v2.0.3) and configure the target URLs - nothing happens.

Should be

I expect to see request sent by the plugin on the target host.

I've checked the targets with manual test requests.
How I can see, if the plugin is working correctly and it fires?
How can I find out, what goes wrong?
Are there special needs to the pipelines to trigger the plugin?

I can't find any hints about this in the docs.
And: The development of the pluging seems to be dead. Maybe there  is a better plugin for this purpose available?