Update (15:40): MailChimp is suffering a global outage. Disable MailChimp immediately on your store if you are experiencing downtime.
Update (15:41): Disable the module using MageRun
mr_examplecom config:set 'mailchimp/ecommerce/active' 0
Update (17:14): MailChimp's service status is healthy again, but it is recommended to remove/disable the MailChimp module from your store due to inherent reliance on MailChimp's API.