None of the 3 Drupal websites on this server are able to show available updates. Error message is:
GuzzleHttp\Exception\ClientException: Client error: GET
http://updates.drupal.org/release-history/addtoany/8.x?site_key=_8FTNSp2dxJwAhgk4-OUW6oti3JrF61GE2q_yozrhak&version=8.x-1.10&list=addtoany resulted in a 403 Forbidden response:
Cannot determine how to diagnose this.