Hi there
Thanks for flagging. You receive a HTTP 403 because you do not have access. This, indeed, is a matter of configuring the CERN Indico Feeds with a new API key. Please see https://drupal-community.web.cern.ch/t/indico-feeds-issue/1528 for more information, or refer to the documentation directly at https://drupal-tools.web.cern.ch/node/118.
Thanks!