Hi there webbro,
I believe you may be using a different plugin than the one I’m able to help out with here in this support forum. It looks like you may be using a custom form or alternate plugin rather than the MailChimp List Subscribe Form plugin we troubleshoot in this forum, as we don’t have a Pro version available of this plugin.
One MailChimp-related plugin I’m aware has a Pro version for purchase is called MailChimp for WordPress here: https://wordpress.org/plugins/mailchimp-for-wp/
Let us know if you have any questions regarding the “MailChimp List Subscribe Form” plugin and we’ll be happy to assist further. Have a great day.
-Kath