Emails Not Syncing to MailChimp

I have been using your plugin for years, we recently built a new site, and moved to a new host. This plugin is no longer syncing contacts to our mailchimp account.

We have tried:
1. creating a new mailchimp API key
2. uninstalling and reinstalling the plugin

No matter what we try the emails are not synced to our mailchimp account. The emails are being stored on our site in the plugin.

Please help