Delivery and retries

Respond with any 2xx status to acknowledge an event. Any other status is treated as a failure. Redirects are not followed.
Each request has a 15 second timeout to connect and a 15 second timeout to receive your response.
Failed deliveries are retried every 5 minutes, up to 10 attempts in total. After the last attempt, the event is not redelivered.
Delivery is at-least-once. Events may arrive out of order, and the same event may arrive more than once.
An event your partner is not subscribed to is skipped, not retried. Subscriptions are checked when the webhook is sent, so a change also applies to webhooks that were already queued. See Event subscriptions.
Each attempt has a new timestamp and signature, so the timestamp cannot be used to detect a repeated delivery. Some events also legitimately occur more than once for the same resource. Make your handlers idempotent: treat each event as a signal to query the resource for its current state, rather than as the state itself.