1. Introduction to webhooks

Numeral 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 Numeral. An update can be the update of any attribute, such as a status, a date, or any other data.

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

2. Event topics and types

Events have a topic and a type. The topic corresponds to the type of the object that has been created or updated. The type corresponds to the exact update on the object.

Topic	Lifecycle events
`payment_order`	Payment order lifecycle events
`incoming_payment`	Incoming payment lifecycle events
`return`	Return lifecycle events
`return_request`	Return request lifecycle events
`inquiry`	Inquiry lifecycle events
`balance`	Balance lifecycle events
`transaction`	Transaction lifecycle events
`counterparty`	Counterparty lifecycle events
`counterparty_account`	Counterparty account lifecycle events
`virtual_account`	Virtual account lifecycle events
`payee_verification_request`	Payee verification request lifecycle events
`reconciliation`	Reconciliation lifecycle events
`expected_payment`	Expected payment lifecycle events
`payment_capture`	Payment capture lifecycle events
`file`	File lifecycle events
`event`	Event lifecycle events

3. Event structure

{
    "id": "35bb6411-290d-478e-a478-2f84146c2ddf",
    "object": "event",
    "topic": "payment_order",
    "type": "executed",
    "related_object_id": "25102c0f-fc25-44e7-9402-cae6d61ad47f",
    "related_object_type": "payment_order",      
    "status": "delivered",
    "status_details": "",
    "created_at": "2023-02-01T17:13:15.087995Z",     
    "data": {
        "id": "25102c0f-fc25-44e7-9402-cae6d61ad47f",
        "idempotency_key": "",          
        "object": "payment_order",
        "connected_account_id": "a0d22970-3b30-44c9-a5ea-fac6707f6b80",         
        "connected_account": "a0d22970-3b30-44c9-a5ea-fac6707f6b80",
        "type": "sepa",
        "direction": "credit",          
        "amount": 75000,
        "currency": "EUR",
        "reference": "Invoice ID 89230927",
        "value_date": "2023-02-01",      
        "originating_account": {
            "bank_code": "SOGEFRPP",
            "holder_name": "SoftwareCo",
            "account_number": "FR7601234567890627967100010",
            "holder_address": {
                "line_1": "1, rue de l'Abondance",
                "line_2": "",
                "postal_code": "69003",
                "city": "Lyon",
                "region_state": "",
                "country": "FR"
            }
        },             
        "receiving_account_id": "",          
        "receiving_account": {
            "bank_code": "BNPAFRPPXXX",
            "holder_name": "PartnerCo",
            "account_number": "FR7601234567891127967100082",
            "holder_address": {
                "line_1": "1, rue de la Bourse",
                "line_2": "",
                "postal_code": "59000",
                "city": "Lille",                  
                "region_state": "",
                "country": "FR"                  
            }
        },
        "direct_debit_mandate": null,
        "status": "executed",
        "status_details": "",
        "auto_approval": false,          
        "reconciliation_status": "unreconciled",
        "reconciled_amount": 0,      
        "metadata": {},
        "bank_data": {
            "file_id": "b251f19a-55a4-459a-8fb0-8dc2b72443d4",
            "message_id": "230201030031Fzmc",
            "end_to_end_id": "25102c0ffc2544e79402cae6d61ad47f",
            "transaction_id": "25102c0ffc2544e79402cae6d61ad47f",
            "original_instruction_id": "25102c0ffc2544e79402cae6d61ad47f"
        },      
        "created_at": "2023-02-01T17:10:00.248706Z",
    },
}

4. Registering an API endpoint

In order to use webhooks, you should create an API endpoint on your server and register it using the Numeral's dashboard. To register an API endpoint, go to Developers > Webhooks > Add webhook.

By default, all event topics and types will be sent to your API endpoint. If you would like to only receive specific event topics or types, please get in touch at [email protected].

5. Event delivery modes

Webhook support multiple event 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, Numeral 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, Numeral 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.

6. Acknowledgment of receipt

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

To guarantee that your API endpoint receives the events in the correct order:

The next event is sent once the previous event has been received
Events are delivered steadily over time one by one
The processing of events stops at the first failed event

The resent failed events feature should be used to resend failed events and resume the sending and delivery of events.

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 up to 5 times during a ~2.8-hour period using an exponential back-off strategy. The event is set to failed status after 6 unsuccessful deliveries.

8. Webhook event idempotency

In order to guarantee that each event is unique, every webhook payload includes an idempotency_key attribute within its JSON body. Additionally, when a webhook 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 errors.

9. Verifying webhooks

Webhooks sent by Numeral are signed so that you check that they have not been modified in transit and verify their authenticity. They also originate from a limited list of IPs. Check our dedicated guide to learn how to verify webhooks.