Most-likely the tool won’t support tls1.2/1.3 which comes in with v11. Should be easy to check if it is a tool problem - run the session relevance directly via a browser (https://url-to-bigfix-root:52311/api/query?relevance=URI_Encoded_Session_Relevance) or try some more-dedicated tool suited for the job (Postman or something along those lines). If it works with other methods but not through what you are running then it’s a clear interface/tool problem…