No response message shown

I believe I have everything set up correctly, since I am receiving the double opt in email from mailchimp, however, I never see a success message displayed on screen. The AJAX call is responding with a 200, but the response body is simply null.

My form code is as follows:

<span class="your-email">
	<input class="wpcf7-email" type="email" name="EMAIL" placeholder="Enter your email" required />
</span>

<span class="sub">
    <input type="submit" value="Subscribe">
</span>

<span class="email-lists">
    <label>
        <input name="_mc4wp_lists[]" type="checkbox" value="########"> <span>List 1</span>
    </label>
    <label>
        <input name="_mc4wp_lists[]" type="checkbox" value="########"> <span>List 2</span>
    </label>
</span>

Any thoughts as to why I’m not seeing a success message? I tried adding in {response} after the email-lists span, but that didn’t seem to make any difference.