What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Have you tried following this guide on how to integrate MailChimp to your JotForm form: https://www.jotform.com/help/163-How-to-Integrate-with-MailChimp?
In the MailChimp integration wizard, you'll need to add your API key that you got from your MailChimp account:
If it is valid, hit the "Authenticate" button. Then complete the other settings.
Let us know if you are still unable to make this work.