> ## Documentation Index
> Fetch the complete documentation index at: https://docs.authsignal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Delivery and retries

> How Authsignal delivers webhook events, and what happens when delivery fails.

## Synchronous webhooks

Sent during an active request. The response affects the outcome of that request, so respond as quickly as possible and defer slow work to a background job.

* **Challenge events** (`email.created`, `sms.created`, `push.created`). A non-2xx fails the challenge and an error is returned to the caller. The [pre-built UI](/implementation-options/prebuilt-ui/overview) prompts the user to retry; the SDK or API surfaces the error to your application.
* **Action verification** (`action.verify`). A non-2xx or a timeout blocks the transition to `CHALLENGE_SUCCEEDED`. No automatic retries; the user can retry by re-running the verification.

## Asynchronous webhooks

Sent in the background, so they do not block the originating request.

* **Authenticator events** (`authenticator.*`). When your endpoint returns a non-2xx response, the event is retried up to **3 times**, with a minimum of **30 seconds** between attempts.
* **Log events** (`action.log_created`, `challenge.log_created`). Delivered in batches of up to **500 events** after your tenant's challenge token duration (typically 15 minutes). Failed batches are retried periodically until delivery succeeds.

Both types use **at-least-once delivery**, so the same event can arrive more than once. De-duplicate using the envelope `id`. Authsignal also does not guarantee strict ordering, so use the `time` field on the envelope to reconstruct order if you need it.

## IP address allow-listing

Authsignal will send webhooks originating from the following IP addresses:

| Region        | IP Addresses                                                          |
| ------------- | --------------------------------------------------------------------- |
| US (Oregon)   | 44.224.97.232<br />44.230.210.235<br />44.236.208.22<br />52.33.85.88 |
| AU (Sydney)   | 13.210.81.243<br />3.105.80.107<br />54.252.129.142                   |
| EU (Dublin)   | 34.247.148.106<br />34.253.116.90<br />54.171.116.55                  |
| CA (Montreal) | 16.52.98.180<br />16.54.49.43<br />16.54.18.28                        |