# CallbackHandler Overview

The CallbackHandler allows customers to receive callbacks, if desired, by creating an endpoint that implements our specified type for callbacks. If they choose to not implement a callback endpoint, documents can be retrieved manually through the corresponding Get method.

## External Callback Overview

Users supply the Callback URL, Username, and Password with the Select And Generate API to integrate with IEDocService in Expere Document Services.

The delivery service uses "IStatusUpdateSink" to display a CallbackHandler Type of "GenerateUpdate." To use callbacks with Select And Generate API's, integrators should implement "HandleUpdate" for "IStatusUpdateSink."

## Sample Callback Handler Scenario (SelectAndGenerate)

    CallbackHandler:
    Type = GenerateUpdate
    Description = Always blank.
    DeliverResponseService: NA

## SelectGenerateDeliver Callback Overview

Users supply the Callback URL, Username, and Password with the SelectGenerateDeliver API to integrate with IEDocService in Expere Document Services.

The SelectGenerateDeliver method utilizes two callbacks:

- IDeliveryResponse provides status updates as the package advances through the print fulfillment process.
- IStatusUpdateSink alerts the user to any errors consisting of the error status and description.

To receive both callbacks above, integrators must implement both interfaces on the same endpoint.