The goal url registration allows you to know how many visitors went to your success page (signup, payment, etc.) after receiving an email reminder.
You can set a goal url for each of your popups.

How to set it
1. Log in to your account
2. Create a popup or edit one that already exists
3. Select the “Email reminder” tab
4. Look for the “Goal (optional)” section at the bottom of the page and enter your goal url
5. Click on the “Save and close” button

That’s it, your goal url is set!