"Referrer plugin not enabled" on Reporting API

Reporting API is responding to a request for getCampaigns, “The plugin Referrer is not enabled. You can activate the plugin on Settings > Plugins page in Piwik”. When I go to look at the plugins page, it is active (see below).

here is the request I’m making to the API:
curl -i -k -X GET ‘https://piwik.****.com/analytics/index.php?module=Referrer&method=Referers.getCampaigns&date=today&period=day&idSite=2&format=json&token_auth=’********’’


the name of the plugin is Referrers. The module parameter is missing an s.

So the URL should look like this:

See also The plugin Action is not enabled.