When you start creating an MailChimp Zap, you will be prompted to connect a New Account:
You should then get a pop-up window from Mailchimp asking you to log-in to authorize the connection between that Mailchimp account and Zapier.
After logging in, you'll get sent back to your zap where you now have your Mailchimp account connected!
If you use Google Apps to access your Mailchimp account, you'll need to set up a username and password with Mailchimp. Here's a link to their guide on doing so: http://kb.mailchimp.com/integrations/other-integrations/integrate-google-apps-with-mailchimp
After you have a username and password, you'll be able to log into your Mailchimp account when trying to connect it to Zapier to ensure that connection is made.
You'll never want to actually type an actual email address into the forms Zapier gives you. The magic of Zapier is pulling data from the trigger service and putting that data into the forms via our handy variable insertion:
If your Mailchimp list has double opt-in enabled, you won't see any subscribers added by your zap until after that new subscriber clicks through the double opt-in email. However, your task history will show a successful task immediately, even if the subscriber does not confirm the double opt-in email.
Mailchimp checks for duplication based off email address, so any email addresses your zap is trying to add that already exist in that list will have a "halted" status in your task history. If you want to update the subscriber, you need to change the Updated Existing field to "Yes."
If someone was subscribed to a list, then unsubscribed, and later was added back to the list, the zap will not trigger as it sees it as a duplicate from the first time they subscribed. Unique email addresses will only be sent once.
Mailchimp sometimes will return an error requesting an API key value when operating on lists. This often is not because Mailchimp actually needs an API key, but rather that a different error has occurred. Most frequently, this is due to the email provided to Mailchimp containing invalid characters (newlines, quotes, etc.)
If you are seeing this error it means you don't have interest groups enabled. See this tutorial on how to get enable it.
MailChimp requires that you put two spaces between each component of the address field. It should look like this:
If the field is mapped, this likely means that the sample record from your trigger data didn't have anything populated in the email field. While the field is mapped correctly, there is no data being sent in the email field, which causes an error.
For example, if you are using the Pipedrive New Person trigger but the person pulled into your trigger sample doesn't have the email filled out, you'll see this in the trigger data:
To fix this, go into Pipedrive and create a brand new person with an email filled in. Back in Zapier, click "Re-test Pipedrive to get another person" and then finish testing the MailChimp action. Same thing would be applicable to a different app and trigger.