GET call not working on mock service for free version of Stoplight

Hi,
I have a simple API set up with the free version of Stoplight, after publishing the API and setting up the mock service I get a 422 error on the GET call , all the other calls work fine - is this is known bug or is there a setting I need to change?
I can see that the curl request is not pulling in the request parameters for a GET. 
Thanks