Listing sites "Error(GSMSITE009):Not a GSM Console"

Hi everryone,
 
I'm trying to use the API for listing sites and theat history. I'm able to login correctly and obtain both the access and the refresh token. However when I try to list the sites using the GSM KEY, I get a 400 status code with error descrioition
 
Error(GSMSITE009):Not a GSM ConsoleShould I contact the customer support or I'm using the API in the wrong way?
 
(by the way I tried also using the Powershell snippet of https://community.webroot.com/t5/Unity-API-forum/Simple-PowerShell-example-to-get-site-info/td-p/309151 )
 
Thank you very much!