FTP Error 530 User cannot login

In my case I forgot to enable the Basic authentication

Have you tried logging in from the FTP server? If you do this, and have "Show detailed messages from local requests" enabled under FTP Messages, then you'll get a clearer idea as to why the login if failing. In my case I got the following message (I am using IIS Manager Users, and Passthrough authentication)

530-User cannot log in.
 Win32 error:   Access is denied.
 Error details: Filename: \\?\C:\Windows\system32\inetsrv\config\redirection.config
 Error: Cannot read configuration file due to insufficient permissions

To solve this I gave the NETWORK SERVICES user read only access to the config directory specified in the error message. I'm not 100% sure this is the right thing to do, but it certainly fixed this issue for me.

Try submitting your credentials in this format:

UserName: Domain|Username
Password: secretSquirrel

in my situation, I was missing Role Service FTP extensibility, which is actually allows IIS Manager Auth. This is pretty tricky, as you could allow IIS Manager auth, but still it would not work until you have not installed FTP Extensibility