It would be nice if you could specify an “extern id” when you create a batch transcription request and that the “external id” is also returned in the response of the web hook callback.

Why? To be able to link a request to an id of a running process/workflow. For example in a durable function. The durable function (using a orchestration) looks like:
1. Durable function send a message to the speech to text service (STTS) to create a transcription.
2. Durable function makes a call to context.WaitForExternalEvent<string>("TranscriptionCompleted");
3. At some point in time the STTS is finished and calls the web hook.
4. The web hook gets the message, but it only contains the transcription id, so it has no knowledge to trigger the correct durable function (sendEventUrl), because to be able to send the TranscriptionCompleted event you need to know the instance id of the durable function.

Of course there are way to solve this “problem” now, for example by creating a mapping table between the transcription id and the durable function orchestration instance id. However this could be potential an a problem is you want to listen for the TranscriptionCreation event, because that could potential be fired before a mapping is created in the mapping table (because you first need to create the request before you can store the transcription id).

So a nice solution for this, is to be able to specify an external id.