How to Get MailChimp API Key
To use Contact Form 7 MailChimp Extension, you need to obtain your MailChimp API key, follow these steps to find it.
Users with Manager permissions can generate and view their own API keys. Users with Admin permissions can also see API keys for other account users. Below, you’ll learn how to grab an existing API key or generate a new one.
Login to your MailChimp account here: https://admin.mailchimp.com/account/
Once you click the link highlighted (yellow) above you will be presented with the API key at the bottom of that page
Input your MailChimp API key in the appropriate field inside To use Contact Form 7 MailChimp Extension
I hope this was a useful explanation of how to get a MailChimp API Key to use with Contact Form 7 MailChimp Extension.