If you wish to charge your customer on the basis of their usage of your API Product then you will need to report the usage to Stripe.
There are two ways to accomplish this.
Report the usage yourself
This is useful if you have a complex API Product with multiple rules on how the billing will take place or you plan on using a different unit of measurement than No. of API Calls.
Automatically report API Usage
With the Usage Events Add-on, Apiable will report the usage on your behalf. Find out how to set up automatic reporting to Stripe