1. Introduction to webhooks

Mambu Payments uses webhooks to notify your application when an event is created. Webhooks are particularly helpful for asynchronous events, such as a payment being executed by the bank or an account statement being received from a bank.

Events are created when an object is created or updated, either by a user using the API or the dashboard or by Mambu Payments. An update can be the update of any attribute, such as a status, a date, or any other data.

For each event, Mambu Payments will send a POST request to your API endpoint in JSON format. This API request contains an event object.

2. Registering a webhook

In order to use webhooks, you should create an API endpoint on your server and register it using the Mambu Payments dashboard. Learn how to add a webhook.

3. Event delivery modes

Events support multiple delivery modes.

Delivery mode	Order guaranteed	Throughput	Default delivery mode
Individual events	Yes	Base	✅
Batched events	Yes	High	-
Parallel individual events	No	High	-
Parallel batched events	No	Highest	-

The order is defined as the order of events for a given object, based on its lifecycle.

To guarantee order, Mambu Payments waits for the acknowledgment of receipt of an event before sending the next event. This means, for instance, that a payment_order.processing event will always be sent before a payment_order.sent event, as per the payment order lifecycle.

There are some edge cases where the order of the messages delivery is not deterministic (or might not be as you expect). For example, if you create a payment order via a sync HTTP API call, you may receive a notification that the payment order is pending_approval even before you get a response for the sync HTTP API call to create the payment order.

When events are sent in parallel, Mambu Payments does not wait for the acknowledgment of receipt of an event before sending the next event. As a result, order is not guaranteed. As an example, payment_order.sent might be delivered before payment_order.processing event.

The maximum number of events in a batch is currently set to 100 for deliverability and performance reasons. Higher limits can be discussed on a case-by-case basis.

Contact us at support@numeral.io if you would like to receive events other than as individual events.

4. Webhook idempotency

In order to guarantee that each event is unique, every webhook payload includes an idempotency_key attribute within its JSON body. Additionally, when an event is sent individually, the TX-Webhook-ID HTTP header is set to the value of the idempotency_key.

The idempotency key is unique for each event / webhook combination. Therefore, if an event is sent multiple times, it will always carry the same idempotency key value, avoiding duplication error

5. Verifying webhooks

Webhooks sent by Mambu Payments always originate from the same IPs. They can also be signed and authenticated with an API key or using OAuth2.0. Learn more in the dedicated guide.

6. Acknowledgment of receipt

To acknowledge the receipt of an event, your API endpoint must respond with a 2xx HTTP status code to Mambu Payments within 5 seconds.

7. Exponential back-off strategy

If your API endpoint takes longer to respond or returns an HTTP status code different from 2xx, the event will be set to pending_retry status and re-sent using an exponential back-off strategy. The delay between retries doubles each time, starting at 10 seconds.

Retry	Delay from first attempt
1st	10 seconds
2nd	20 seconds
3rd	40 seconds
4th	80 seconds
5th	160 seconds

After all retries are exhausted, the event is set to failed.

A new optional maximum wait time parameter can be configured per webhook. It sets an upper bound on the cumulated time an event will be retried from its first delivery attempt. When this duration is exceeded, the event is marked as failed regardless of the number of remaining retries. This is useful when timely delivery matters more than maximizing retry attempts. If not set, the existing behavior (retry until the number of retries is exhausted) is preserved.

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If the event delivery mode is sequential or batched, Mambu Payments will block the webhook and stop sending events in order to guarantee their order.

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We recommended adding a notification email address when configuring your webhook to be notified in case a webhook is blocked and events are no longer sent.

8. Retry events in case of webhook failure

To retry events after you have fixed your webhook, use the Retry failed events API endpoint or dashboard feature (Developers > Events > Retry failed events).

9. Re-send an event already delivered

To re-send an event previously successfully delivered to the same or another webhook, use the Resend event API endpoint. This can serve different operational purposes like data analysis or reporting.