We recently launched a free usage tier for MMS Backup, our online backup service for MongoDB. We use Stripe to bill customers on a monthly basis via credit card, and we've implemented a freemium model where any bill less than $5 is complimentary. To accomplish this, we utilize Stripe's subscription billing capabilities and employ webhooks to inspect the invoice and apply a negative invoice item if the total bill is under $5. This approach allowed us to quickly launch our free usage tier and offers a solution that can be helpful to others looking to implement a similar freemium model using Stripe.