Google Data Studio Community Connector for Mailchimp Insights
Follow the setup from here to get the OAuth2 working, dont forget to fill in the CLIENT_ID and CLIENT_SECRET at the top of Mailchimp_OAuth2.gs.
There is also the option to put your email address in Code.gs in the function isAdminUser(), this will give you slightly more verbose errors should you encounter them.
Google's Community Connector Guide is a very usefull resource when setting up your community connector, Developer access will also need to be requested before you can use your Community Connector.