- Webhook reliability is the foundation billing integrations depend on most heavily.
- Plan upgrades and downgrades need clear proration logic, not ad hoc handling.
- Failed payment (dunning) flows recover meaningful revenue if built properly.
- Billing state should be the single source of truth for feature access decisions.
Webhooks are the foundation, and they need real reliability
Billing providers communicate state changes — a payment succeeded, a subscription renewed — primarily through webhooks, and a missed or improperly handled webhook can silently desync a customer's actual billing state from what your product thinks it is. Idempotent, reliably processed webhook handling is foundational, not optional.
Proration needs explicit logic, not guesswork
A customer upgrading mid-cycle or downgrading partway through a billing period needs clear, tested proration logic — otherwise customers get billed incorrectly, which generates support tickets and erodes trust in the billing system faster than almost any other issue.
Dunning flows recover real revenue
A well-designed failed-payment (dunning) sequence — retrying the charge, notifying the customer, offering an easy way to update payment details — recovers a meaningful share of subscriptions that would otherwise silently churn due to an expired card rather than an actual cancellation decision.
Billing state should gate feature access directly
Feature access should be checked against the actual current billing state, not a cached or assumed status, to avoid the two most common billing bugs: a canceled customer retaining access, or a paying customer being incorrectly locked out after a billing event.