A payment flow can pass every launch check and still break a month later. The first checkout sends one kind of event, and the renewal often sends a different one. If the handler only knows the first, the renewal lands, gets a polite 200, and nothing extends the customer's access.

So the card is charged on day 31, the provider shows the subscription as active, and the app quietly downgrades someone who just paid. Nobody notices until that customer writes in, if they write in at all.

Worth checking before launch. List every event your provider sends over a subscription's life, like renewals, failed payments and cancellations, and make sure each one is either handled or logged loudly. Then run a renewal in sandbox instead of waiting a month to find out 🙂