If your pricing strategy included usage-based pricing, such as per API, per requests, per orders, etc, you might want to record the actual usage of your customers so they will be billed properly at the end of each cycle. This is done through Stripe. Stripe allows you to record the usage of a customer to their subscription through their powerful APIs.
If you are using recurring quantities and want to change the number of units a customer is at like “per-seat licensing”, you need to update the quantity on the Plan.
For an in depth guide on handling subscription quantities check out this guide.
There is a Stripe API call for creating a usage record, which is how you add to the metric you're billing against. You must store the subscription item ID on your database because it is used to update the usage of a metric. Any metrics you update will be reflected in the Billflow Subscription Management Portal for your customers to see.
For an in depth guide on handling metric based check out this guide.