You built the product. Now it needs to charge for it.

Stripe is the easiest payment integration in the world — until it isn't. The basic credit card form is straightforward. The subscription lifecycle is where most implementations develop bugs that cost real money: the subscription that transitions from trial to paid but the feature gate doesn't update; the failed payment that retries but the user doesn't know to update their card; the cancellation that removes access immediately instead of at the end of the billing period; the plan upgrade that charges the proration correctly but doesn't unlock the new features.

The other common failure: webhook handling. Stripe's webhooks are the mechanism by which Stripe tells the application what happened in the billing system. Every significant billing event — subscription created, subscription updated, payment failed, subscription cancelled — fires a webhook. Applications that don't handle webhooks correctly develop billing state inconsistencies: the application thinks a subscription is active when Stripe has it cancelled, or vice versa. These inconsistencies cause access control bugs (users who cancelled can still access paid features) and support tickets.

The correct architecture: Stripe is the source of truth for billing state. The application maintains a local cache of subscription status (populated from Stripe webhooks) that's used for feature gating. The webhook handler processes every relevant Stripe event and updates the local billing state accordingly.