Usernames with spaces don't work.

[ThatDude79]

If the username has a space, that is not checked and replaced with %20 for a valid URL
"http.client.InvalidURL: URL can't contain control characters." " (found at least ' ')"

A temporary user workaround is just to replace the " " with "%20" in the Username field of the Settings/API Keys tab.
"User Name123" will not work
"User%20Name123" will work

This mat be an issue with other characters if any other control characters can be in a booru username