Beware the uncapped pay as you go

With plain Pay-as-you-go API subscription plan, it’s easy for the customer to end up in a situation like on the following invoice:

The customer is subscribed to a plan with a soft quota of 1000 calls per month.

“Soft quota” means that the limit serves purely informational purposes and after reaching 1000 API calls the customer can continue making calls over the defined limit and potentially get a huge bill at the end of month.

The pricing on this plan is $300 monthly fee + $1 per API call.
Therefore, after 8749 API calls the bill has grown tremendously.

There are many possible reasons for excessive usage: a bug in customer’s software, oversight, lack of monitoring, cat stepping on F5, etc.

For your customer to be on the safe side, implement the cap. Negotiate with the customer what maximum usage is acceptable and implement that hard limit.

If you’re using Project X for API monetization, it’s as simple as setting the checkbox “Is hard limit” on the quota and attaching a metered price to that quota.

Configured this way, Project X billing engine will keep track of the actual usage and translate that data into amounts on the invoice.

In turn, due to the hard quota, Project X API Gateway will prevent the customer from making excess API calls over the set limit. As a result, the customer will still be charged for the actual usage but will never exceed the cap.