got the same problem! I’ve updated my Mailchimp plugin because it doesn’t recognize the new api from mailchimp now every time I try to subscribe it says “Oops. Something went wrong. Please try again later.”
I have the same lists on my Mailchimp
Email Address | EMAIL
First Name | FNAME
on my wp plugin
<input type="text" class="icon-user" name="FNAME" placeholder="Name">
<input type="email" id="mc4wp_email" class="icon-envelope" name="EMAIL" placeholder="Email" required /><input type="submit" value="SUBSCRIBE"/>
Thanks for help