After adding a new MailChimp List into MailChimp, you'll need to refresh the Lists in HealCode so that the new List is available to the Prospect Widget and Registration Widget.
- Create the new List in MailChimp
- Login to HealCode
- Click on your name in the top-right corner > Manage Connections
- Click "Refresh your lists" in the MailChimp section
Your new list can now be selected for the Registration Widget or Prospect Widget.