# Imported Numbers and Hosting Orders Callbacks

You can set up callback URLs to receive event notifications when your numbers are updated. 

When delivering events the order is not guaranteed (for example, a failed event scheduled for retry will not block other events that were queued).

The client's callback handler must implement the state machine that can decide what to do with _unexpected_ events, for example, "old" events or invalid state transitions. In these cases the handler could use the API to GET the latest state for the resource.

The callback handler is expected to "ingest" the event and respond with 200 OK. The domain-specific business logic and processes should be executed outside of the callback request, as internal asynchronous jobs.

To use callbacks, add the following IP addresses to your allowlist:

- 54.76.19.159
- 54.78.194.39
- 54.155.83.128



## Get callbacks configuration

 - [GET /v1/projects/{projectId}/callbackConfiguration](https://developers.sinch.com/docs/numbers/api-reference/imported-hosting/imported-numbers-and-hosting-orders-callbacks/getcallbackconfiguration.md): Returns the callbacks configuration for the specified project

## Update callback configuration

 - [PATCH /v1/projects/{projectId}/callbackConfiguration](https://developers.sinch.com/docs/numbers/api-reference/imported-hosting/imported-numbers-and-hosting-orders-callbacks/updatecallbackconfiguration.md): Updates the callbacks configuration for the specified project

## Event notification

 - [POST EventsCallback](https://developers.sinch.com/docs/numbers/api-reference/imported-hosting/imported-numbers-and-hosting-orders-callbacks/importednumberservice_eventscallback.md): A notification of an event sent to your configured callback URL.