Lago
Open Source Metering and Usage Based Billing API
... with coupons that customers can redeem to get a discount. Lago allows you to create one-time charges that are invoiced on the fly. Depending on the configuration of your plans, Lago automatically calculates what each customer owes you and generates invoices. Unlock recurring revenue opportunities for pay-as-you-go pricing models with Lago’s real-time prepaid credit features.