View source for Ninja Forms - Mailchimp plugin

All forms going to mailchimp need to have the following fields and they need to be required.
First Name
Last Name
Email

Setting Mailchimp API Key in Forms > Settings > Mailchimp
This is found in your MailChimp "Extras" setting and looks like this: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx-xxx

Each form also might need to have the Double Opt in checked in form settings