TL;DR: This is because the second billing year will have a $0 amount.
To check for details, please click the Manage Plan button. The Manage Plan feature in your Subscription settings shows what subscription you're on, as well as the next billing date and amount, so that you can get all the information you need on current and upcoming charges.
First, go to your Settings --> Subscription, then click "Manage Plan" as shown below:
Which will then take you here:
This page will show when your subscription ends, what the next payment date and amount will be, and other relevant information. You can also update your payment method here (adding or removing cards on file), as well as your billing information. Your invoice history will appear here as well:
Note: if you are on any promotional discount, this page will show the billing amount based on the promotion you signed up for (e.g., 2nd year of subscription that is free will show $0.00 for your subsequent charge)