I’ve just installed LFP on an empty WP site, set up a flow to include adding subscriber to a MailChimp list (MailChimp set up with API and seems happy). Flow published. When I test the flow I am not getting added to my MailChimp list.
If you’re using an external flow, and have it set up similar to the screenshot below you should be fine. You would need to receive a confirmation email from MailChimp first, click on the link therein, and then you would be added to the list.
You would not need to edit the sample LeadsFlow Pro mail code. The issue is receiving that confirmation email from MailChimp and then clicking on the link. Then you would be added to the MailChimp list. There might be an option to disable this feature in MailChimp, but that could well be only if you have a paid list.
You may want to speak with MailChimp support for more details on that…