I set up vsftpd on my Ubuntu 20.04 server. Everything worked fine, I was even able to configure TLS. Now, I don't want the users to use SSH. I also disabled SFTP because of that. I don't want to disable SSH for these users because I want them to use it for some basic tools like change the password, etc. So, I've created a custom shell with these tools. However, when I enable this shell for the users, they can't log in to FTP. It just shows "login incorrect".
Why does vsftpd do that?