What am I missing from the report chart tag? What else is needed? Looks ok based on Release notes on report charts documentation.
<apex:page standardController="Account" extensions="AccountTeamChecker" rendered="{!renderELEMENT}">
<analytics:reportChart reportId="00OU0000001rGcq"></analytics:reportChart>
</apex:page>
Produces the error in the post title: Error: Unknown component analytics:reportChart ID is a valid report id. I am not even trying to use a field filter yet.