Cannot find a way to make Piwik work on NC12

I am running Nextcloud 12 on Freenas 9.10 within a jail.
I have tried installing Piwik, but cannot find the way to access it or make it work.

I installed Piwik by enabling the app under the Admin page.
Under /settings/admin/additional, I tried to set the options for “Piwik Tracking”.

According to Piwik documentation, “Site ID” is supposed to be 1.
I don’t know what to write into “Piwik Url”, the blank box only show a partial example of Url.

What is done when the app “Enable” button is pressed? Does it install Piwik and all other optional servers Piwik might need?

What should I be looking for?