adamcrowley on "[Plugin: MailChimp for WordPress] '403 forbidden' if user already subscribed"

URL: http://www.meetingroom.co.nz
MailChimp for WordPress v 3.1.7
Wordpress v 4.5.2
PHP v 7.0.5

The form works as expected when a user initially signs up to the mailing list.

But if they are already subscribed, a '403 Forbidden - You do not have permission to access this document' page is displayed instead of the Already Subscribed message.

Thanks
Adam

https://wordpress.org/plugins/mailchimp-for-wp/