payments-and-billing

Payments and billing architecture for a solo maker - payment provider categories (merchant of record versus payment processor and what each handles for tax, VAT and chargebacks), choosing one, checkout flow design, webhooks with signature verification, idempotency, replay and ordering, the subscription state machine (trialing, active, past_due, canceled), entitlements stored in your own database and derived from events, never trusting the client, test mode, reconciliation jobs, refunds, tax and invoicing flagged to verify, avoiding PCI scope by never touching card data, secrets handling, failure modes and dunning. Load when integrating payments, handling webhooks, modelling subscriptions or entitlements, or debugging billing state.