Build or fix my dunning flow: what happens between a failed subscription payment and losing the customer. Check what the provider retries automatically and what my app does on top. Implement: on payment failure, an immediate email to the customer saying the charge failed, with a direct link to update their card (a page that works without friction: logged in or a signed token link, straight to the card form); follow-ups over the retry window (day 1, day 3, day 7 is a sane default) with escalating clarity about what happens next (access pauses on date X); the card update page wired so a new card triggers an immediate retry of the failed invoice where the provider supports it; and a final notice when the subscription is actually canceled, with a resubscribe path. Suppress the sequence the moment a retry succeeds, and send a 'you're back' confirmation instead. Use the email system already in the project. Don't send dunning emails for one-time purchases. Don't threaten or use fake urgency; state dates and facts. Coordinate with the provider's built-in dunning if it's enabled so the customer doesn't get double-emailed from both systems. Deliver: the email sequence with timing, the card update flow, the retry trigger, and a test: fail a payment with the provider's test card, walk the sequence, update the card, and confirm recovery and the confirmation email.