Wix calls this method to retrieve the initial charge limit for a paid instance of your app. This happens every time a customer is upgrading to a paid version of your app.
You can't update the charge limit after you've set an initial value. Customers can increase the limit in their site's dashboard, currently they aren't allowed to decrease it.
Note: This feature isn't yet available to all users. Your app can have only 1 usage-based plan and no other plans. To add a usage-based plan to your app, submit a request to add a usage-based plan.