How to let AMS know about failure during invoke processing

In an AMS APP, how do we return Failure back to the AMS? In the InvokeServices(Without Data) we send the response straight away after validation the main request.

Then we export all the data and process it. Completion Callback Endpoint - This is called on Success.

My question is what to do when the things go wrong during processing. How to let AMS know to fail the program?

Thanks

Rajat