MailChimp signup source URL

I use a custom signupform from MailChimp and try to add a field that would show which url the person subscribed from.

Following multiple tutorials I have tried:

<input type="hidden" name="source" value="<?php echo $_GET['data']; ?>">
<input type="hidden" name="source" value="{data key="source"}" />
<input type="hidden" name="source" value="URL">

However, I can´t manage to retrive the URL using MailChimp for WP plugin by ibericode.

Thankful for help

via Chebli Mohamed