Just to be clear, you want to use the API from an external process NOT a robot?
You would instantiate the job using an API.
You would consume the outcome of the job using the GET equivalent, having the data passed back out as an argument.
To do the ‘the robot has finished’ part you might be able to use webhooks but it’d be ugly.
Would suggest having the RPA process generate a service bus (if azure) message which would automatically trigger the follow on job.
Otherwise yeah, you’ll have the potential for a service waiting up to 24hours for a response like Jon suggested.