Your origin server probably isn’t configured to know about the www name, so it refuses to answer to that name. I have no idea what “switchy” is so I can’t provide any insight into setting that up.
Your page rule, though, should work if you enable the proxy for the www DNS entry.
If you want to forward with the path, you need the destination to be http://shostel.org/$1 (or better https://shostel.org/$1 to do the HTTPS redirect at the same time)