billing-automation

Create a Subscription class tracking status, current period start and end dates, then run a billing cycle processor that generates an invoice, charges the customer's saved payment method, and advances the period on success. On failure, mark the subscription past_due and start dunning.

Use a retry schedule such as 3, 7, and 14 days after the initial failure, sending a notification email at each step. If payment succeeds, reactivate the subscription; if all retries are exhausted, cancel the subscription and notify the customer.

Divide each plan's amount by total days in the period, then multiply by remaining days to get the unused credit on the old plan and the charge for the new plan. The net proration is the new plan charge minus the old plan credit.

Yes, usage records are tracked per customer and aggregated over the billing period. Charges can be computed with per-unit, tiered, or volume pricing models and added as invoice line items alongside the base subscription fee.

Tax jurisdiction is determined from the customer's country and state, then a rate lookup applies the appropriate percentage to the invoice subtotal. US states use sales tax, EU countries use VAT, and Australia uses GST.

The code provides patterns rather than a production service: PDF generation, VAT number validation, and payment processor integration are stubbed. You must connect a real payment gateway like Stripe and persist subscription and invoice state in a database.