Yes, it's sh.itjust.works, I put in my username and password and it just says invalid login. I even checked my password with the web version of the instance and the password is right
You might have to add "https://" in the beginning, but I doubt that that's it. What version is shitjustworks running on? Could be possible that sync can't log into older versions. Either that or the instance is just too overloaded.