<MailchimpHandler>
    <add key="baseUrl" value="https://usX.api.mailchimp.com/3.0/"/>
    <add key="apiToken" value="6bf320e2d9601cddb2de577428649b8c-us4"/>
  </MailchimpHandler>
OF
<MailchimpHandler baseUrl="https://usX.api.mailchimp.com/3.0/" apiToken="6bf320e2d9601cddb2de577428649b8c-us4" />