[Windows Client] Every time I try to create a new account on my self-hosted server, I get an "unknown error"

[sloppy-carlton]

I've edited the Windows registry exactly as the instructions said (setting selfHosted=true and serverHost to my server's url and port number in HKEY_CURRENT_USER\Software\Librum-Reader\Librum after running the client software once). My server is running inside a Docker container hosted on a remote computer that I'm accessing via a Tailscale subnet router, so I should be able to just put in the local IP of the server and the http port number and be good to go, right? Unfortunately, I can't seem to get past the account creation page without an unknown error occurring.