The problem was resolved in subsequent private correspondence. MohammedAzim Shaikh reports:
I tried removing all the ‘cURL blocked host list’ and found the issue was solved. My Jobe server IP is ‘192.168.xxx.yyy’, and the cURL blocked host ‘192.168.0.0/16’ was blocking the connection. I removed that particular entry and ran the code runner and finally it worked.
For the benefit of other readers with similar problems, the cURL block host configuration is at Site administration > HTTP security > cURL blocked host list. The default is specified to block various common internal network or cloud provider hosts. There's a potential confusion here if the field on that page is left blank: does that mean the default values are used, or does it mean no hosts are blocked? I suggest when testing that you try copying the default values into the textarea, but delete any that might be problematic.