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Why payment webhooks can be duplicated
Webhook delivery is designed to survive temporary failures. A provider may retry when it does not receive the response it expects, and a delivery can reach your endpoint even when the provider did not receive your earlier acknowledgement. Stripe says an endpoint may occasionally receive the same event more than once; PayPal describes at-least-once delivery in its invoicing webhook guidance; and Adyen warns that duplicate notifications can occur. Stripe, PayPal, and Adyen all document duplicate handling.
There is no universal retry count or deduplication field: behavior depends on the provider and the product or webhook flow. For example, Stripe documents live-mode retries for up to three days with exponential backoff, plus manual resends from the Dashboard for up to 15 days and the CLI for up to 30 days. PayPal’s REST integration guide says unsuccessful deliveries may be retried up to 25 times over three days; that policy is distinct from the invoicing guide’s duplicate-event advice. Check the current documentation for the specific webhook product you use.
What identity should you use to detect a duplicate?
Use a stable identifier that matches the provider’s event model and the business effect you need to protect. Do not assume a field that works for one provider—or one type of duplicate—works everywhere.
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| Provider and scope | Duplicate identity guidance | Delivery or ordering detail |
|---|---|---|
| Stripe | Track the event ID to identify repeat deliveries of the same Event. Stripe notes that separate Event objects can sometimes represent duplicates; for that case it recommends the object ID in data.object together with event.type. |
Live-mode retries run for up to three days with exponential backoff. Manual Dashboard resends are available for up to 15 days and CLI resends for up to 30 days. Stripe does not guarantee event order. Stripe documentation |
| Adyen | Notifications with the same eventCode and pspReference can be duplicates, even if eventDate or other fields differ. Adyen advises using the latest webhook event details. |
Adyen says it queues a webhook for retry if it does not receive a response within 10 seconds. Some webhooks include a sequenceNumber; check timestamps and sequence where available. Adyen documentation |
| PayPal invoicing webhooks | The event id is a unique identifier that can be used for deduplication. |
The invoicing guide describes at-least-once delivery. PayPal’s broader REST integration guide separately documents retries for unsuccessful deliveries. Invoicing guide; REST integration guide |
These are provider-specific examples, not interchangeable rules. A payload hash is generally a poor substitute for a documented identity: a legitimate event can have changed fields, while distinct events can describe related states. For Stripe, deduplicating only by event ID will not catch the separate-Event case it describes; whether to also use object ID and event type depends on the business action being protected.
How to build a duplicate-safe webhook handler
- Receive the request and verify its signature. Validate the provider’s signature using its documented method before trusting the payload or making business changes. Preserve the raw request body if the provider’s signature verification requires it. See Stripe’s webhook guidance and Adyen’s handling sequence.
- Derive the right identity. Record the provider and relevant account or environment scope along with the provider-specific event identity. If you protect a business effect that can be represented by more than one event, define a second business-level uniqueness rule deliberately rather than assuming every event ID is equivalent to that effect.
- Claim the event atomically. Insert a durable inbox record under a unique constraint, or use an equivalent atomic claim. A plain “look up whether it exists, then insert” can race: two simultaneous deliveries may both see no record and both proceed. PayPal’s invoicing guide illustrates unique event storage and transaction-based processing as duplicate mitigations.
- Make acceptance recoverable before acknowledging. In the same transaction as the event claim, enqueue work or record a state from which a worker can reliably resume. A transactional inbox/outbox pattern helps prevent a crash between acknowledging the provider and saving the work. Adyen documents the sequence verify, store in a database or queue, acknowledge, then process business logic; Stripe advises responding promptly and deferring complex work. Follow the exact status-code and timing contract for your endpoint—one provider’s deadline or accepted response is not universal.
- Process asynchronously and protect side effects. A worker should process only a successfully claimed event. Make downstream operations—such as issuing a credit, sending a fulfillment request, or recording a ledger entry—idempotent where possible, and persist processing outcomes so failures can be retried without repeating completed work.
- Monitor and reconcile. Keep enough identity, status, attempt, and error information to diagnose a stuck event. Reconcile important payment state against the provider’s authoritative object or API rather than assuming that one webhook receipt is the entire history.
A practical inbox record
A webhook inbox table commonly stores provider and account scope, event identity, event type, received time, processing status, and the result or error of processing. Put the chosen identity under a database uniqueness constraint. This is an implementation pattern, not a schema mandated by every provider. Retain deduplication records for at least as long as your system can receive retries or manual replays; the appropriate retention depends on provider behavior and your own recovery window.
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Duplicates, repeated business events, and outbound retries are different
Three situations are easy to confuse, but require separate controls:
- Same event delivered again: The provider retransmits one event. Prevent repeat processing with its stable event identity.
- Distinct events describe related or repeated state: The provider emits separate event objects, perhaps for the same underlying object. Decide whether each event represents a new action or merely a state update; use event type, object identity, and current state as appropriate.
- Your application retries an outbound payment request: This is a request from your system to the provider, not an inbound webhook replay. An outbound API idempotency key can prevent the same API operation from being performed twice, but it does not replace webhook inbox deduplication.
Adyen documents reusing an idempotency-key on an outbound POST to make a retried payment request safe. Its API documentation says keys remain valid for 7 to 14 days after first submission and apply account-wide at company-account level, with regional caveats. Those limits concern outbound API requests—not how long to retain webhook event records. Adyen API idempotency documentation
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Can payment webhooks arrive out of order?
Yes, for at least some provider flows, event order is not guaranteed. Stripe explicitly says events are not guaranteed to arrive in generation order. Adyen recommends checking timestamps and notes that some webhook types include a sequenceNumber. Avoid applying every notification as a blind overwrite: an older state can otherwise replace a newer one. Where order matters, compare a provider-supplied sequence or timestamp when available, or retrieve the current object state before applying a consequential transition.
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What to check when duplicates still cause problems
- Confirm you verify signatures before accepting payload data as authoritative.
- Check whether the deduplication key matches the provider’s documented identity and whether it includes account or environment scope.
- Verify that uniqueness is enforced atomically in durable storage, not only in application-level check-then-act code.
- Confirm a successful acknowledgement cannot occur before the event is saved or queued for recoverable processing.
- Inspect downstream effects for their own retry behavior; a deduplicated webhook can still trigger a duplicate external action if the worker repeats that action after a timeout.
- Review event timestamps, sequence information, and current provider object state when events appear to reverse one another.
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