Using API, I am able to create a case, but when issuing ScreeningRequest I get 401 unauthorised.
Using the same caseSystemId I am able to screen the case using the web interface.
There are a number of reasons why you would get a 401 status request return
Are you using the Postman collection? If so, have you updated the casesystemid in the Postman environment? what group are you using?
Have you read and followed the quick start guide and understand the caseid/casesystemid relationship and where the casesystemid is set and used?
Hope this helps,