# Invoke the Publish Callback

To have the system invoke the callback when the final publish result is available, pass in an instance of the callback class as the second parameter in the `EventBus.publish` call.

First, create an instance of the callback class. For example, we use the `FailureCallback` class that we implemented earlier.

```apex
FailureCallback cb = new FailureCallback();
```

This publish call publishes a list of events and passes in a callback instance.

```apex
List<Database.SaveResult> results = EventBus.publish(eventList, cb);
```

This publish call publishes one event and passes in a callback instance.

```apex
Database.SaveResult sr = EventBus.publish(myEvent, cb);
```

## Callback Status Code

When you publish an event with a callback instance of `EventBus.EventPublishFailureCallback` or `EventBus.EventPublishSuccessCallback` and the publish call is successful, the returned `Database.SaveResult` contains a status code of `OPERATION_WITH_CALLBACK_ENQUEUED` in the `StatusCode` field of `Database.Error`. Also, the event universally unique identifier (UUID) is returned in the `Message` field.

```apex
Database.SaveResult[getErrors=(
  Database.Error[
  getFields=();
  getMessage=d473406e-0922-432a-9088-b8c95ef8b548;
  getStatusCode=OPERATION_WITH_CALLBACK_ENQUEUED;]
  );
  getId=e02xx0000000001AAA;
  isSuccess=true;]
 
```

If the Apex publish callbacks feature is disabled in your Salesforce org, the `EventBus.publish` calls that use callbacks still execute but don’t invoke the callbacks. Also, the returned status code is `OPERATION_ENQUEUED`.