borisrio on "Contact Form 7 with MailChimp"

I have the same question, sorry for being such a newbie.
Where exactly should we place that line of code?
I supposed it was at the Edit Contact Form screen - left side Form field. Here's what I have there:

<p>Your Name (required)<br />
    [text* your-name] </p>

<p>Your Email (required)<br />
    [email* your-email] </p>

<p>[mc4wp_checkbox "Sign-up to our newsletter"]<p>

<p>Subject<br />
    [text your-subject] </p>

<p>Your Message<br />
    [textarea your-message] </p>

<p>[submit "Send"]</p>

Then I went to my website to test the form. The check box appears fine but when I hit send, I got an error message:
"Failed to send your message. Please try later or contact the administrator by another method."

Please help