If you see this error code, it means your list settings has too many required
, so Mailchimp is preventing us from adding new subscribers to your list.
To resolve this issue, either create a new list that only requires the email field or edit the current list to no longer require any additional extra fields.
You can do that on the Mailchimp dashboard
Go into your Mailchimp dashboard
Click "lists" and click the list you want to use
On the list's page, click "Settings" and then "List fields and *|MERGE|* tags"
You will now see a table of all fields, make sure only the email fiel is marked as required
Now test the form on your website using a real email address. Once a subscriber passes successfully, the error will be gone.