I've got a new iPhone and have installed Spotify app which works on my android phone. Trying to login it won't allow me to do so and say Login Error 404. Trying to login through Facebook doesn't work either and I either get the same error message or it says I've already created an account with those credentials. I know that, that's what I'm trying to login to!
Did you create your Spotify account through FB? If so, all you will need to do is click the log in with Facebook button and then enter your details. If you created through an email address, just log in with your username (not your email address) and that should work fine. 🙂