There is no automation, but you can use the manual method below:
- Add a checkbox custom field to your posts for your subscriptions.
- Add that field to your form.
- As soon as the post form is submitted that field gets updated.
- Set the post form in a way that as soon as a submission occurs, the admin of the website will be notified by email: https://toolset.com/course-lesson/send-notifications-when-someone-submits-the-form/
- Then the admin can see if the option is checked/unchecked in the email and add the customer's email to the Mailchimp list.
