IIS FTPS connection error 530

Question

I have IIS FTPS site, so only one FTP site, and I configured in bindings host name to be my fqdn of the server. But when I try to connect from ftp client with username...i get error: 530 Valid hostname is expected. And when I enter my username in format hostname|username it works. Why is it behaving like this when I have only one FTP site. Also, when I delete host name from bindings menu, I can not establish connection in any way.