Just to make sure people using Blue Prism Web Services are clear. Best practice is for your Web Service process to NOT be asynchronous - because it would be bad web service practice to wait for the duration of the business process for a response.
Your Web Service should simply take the request and add it to a Blue Prism work queue - to be worked by a resourcepc that is working that queue. The Web Service response should simply be a flag stating the request was successfully received.
If there is a response required by the business process, this should be designed seperatey (potentially by Blue Prism calling a web service hosted elsewhere to return data).