In order to use Mailchimp integration in Leadfeeder you have to turn on Google Analytics integration in your Mailchimp campaigns.
These steps are done in Mailchimp, not in your Leadfeeder account. You can read these instructions in Mailchimp knowledge base, too.
STEP 1: First click on your profile name and choose Account.
STEP 2: Click Integrations.
STEP 3: Click on Google: Analytics, Contacts and Docs.
STEP 4: Click Authorize Connection.
If you're not already signed into your Google account, you'll be asked to log in. If you have several Google accounts, you can select the one you want to use.
STEP 5: Click Grant access after you log in. You'll return to your Mailchimp account and a success message will appear.
Now you have set up Mailchimp Google Analytics integration for your account.
NOTE: You must set up the integration for every campaign you send, too.
When creating a new campaign, make sure you have checked Google Analytics link tracking checkbox in your campaigns Setup step:
If your Google Analytics link tracking checkbox is unselectable, there's an issue with your accounts Google Analytics integration.
After you've turned on Google Analytics integration in Mailchimp, make sure that you have integrated Mailchimp and Leadfeeder properly, too.