I installed Piwik plugin and fill in the matomo related parameters. Statistics are already available on the matomo system. However, no statistical results can be seen in the statistics of an event.
Have you been able to resolve this issue? I seem to be in the same situation: Matomo successfully receives Indico statistics, but any query from the event admin menu results in empty plots.
First of all, set “Result cache TTL (seconds)” to 1 (not sure if we support 0 to disable it altogether) - otherwise the plugin caches error responses as well, making debugging things massively painful. You might also want to wait whatever duration was there before in case you recently tried the statistics page of an event to ensure the cache expired.
“Piwik API server URL” must be your main Piwik URL WITHOUT any /index.php or similar at the end (IIRC we had a wrong description text below that option in the past)