Thank you for looking into it and trying it out. It seems related to security tokens on sessions. On my browser, to reach the management portal, I had to go through the web hosting's dashboard link before.
My browser can access the direct IP fine, but Freeter can't so it seems the browser cached the tokens and Freeter does not have valid session security tokens or cookies. A way to have user-provided cookies to Freeter for such use-cases could be useful.