MailChimp Integration Error When Entering API Key

When enabling MailChimp Integration for the first time, after entering the API key, there's an error.

The resulting url is:

And the error output is:

Notice: Undefined index: mailchimp_webhooks in plugins/mailchimp-sync/admin_page.php on line 279

Warning: Cannot modify header information - headers already sent by (output started at plugins/mailchimp-sync/admin_page.php:279) in wp-includes/pluggable.php on line 1171

Lots of gotchas in your software.

Interestingly enough, upon returning to the main plugin page, everything seems fine... until the next error!