Why charges are there for a Stamps.com account?

Customer:

I am using Woocommerce and would like to ship USPS priority mail flat rate. Does this mean I need to purchase the Woocommerce stamps.com plugin with USPS, as well as a stamps.com account? Why are there three charges for a Stamps.com account? 1 for the plugin, 1 for a monthly fee, and then 1 for your postage? What does the monthly fee cover? Please advise.

Support:

For using our Stamps.com plugin, you need to have a Stamps.com account.

The monthly charge is incorporated from Stamps.com.

Our Stamps.com plugin cost $69.00. It is a single site license with 1-year free update and support.

Postage will be deducted from your Stamps.com Account.