You can use Ap4 Project Managers for free during a 90-day trial version when you sign up. However you can upgrade your account at any time.
When your 90-day free trial period expires, you will be asked to create a paid subscription in the the Account Settings page of your AP4 installation to continue using the paid service. You will be charged monthly approximately 30 days from the date you make the first payment.
However, if you reach the end of your 90-day trial without choosing a subscription, your account will be put on hold (your projects, files, and data will all stay safe and sound, don't worry) until you choose a subscription plan.
You can cancel your subscription at any time simply by logging in, going to the Account Settings page and clicking the "Cancel my subscription" link.
If you opt to pay once a year in advance for an Enterprise plan there is no part refund if you decide to stop using your account during the year. Once you pay for a year upfront your account will be live for 12 months. After the 12 months you can either re-new for a whole year or pay month by month.