Error : 421 Sorry, cleartext sessions are not accepted on this server

When you receive the above error while trying to connect to FTP then follow the below step , Try to preceed your server host name with ftpes://, like ftpes://updatedlinux.com

btw, what is FTPeS (FTP over explicit TLS/SSL)?

This describes overview of what FTPeS is, and the benefit it provides.

Using FTPeS or FTP over Explicit TLS is fairly simple and straightforward. It doesn’t change anything that you do in regards to how you perform FTP actions. The only change is changing your Server Type from regular FTP to FTPeS.

What is FTPeS? FTPeS is short for FTP over explicit TLS/SSL. TLS and SSL is a means of encrypting data, using a public/private key combination set. This is the same technology that is used to bring secure web browsing (HTTPS) on the web. Note that when you go to purchase an item from a website on the Internet, when you check out most of the time you are taken to a secure website, verified by the HTTPS in the browser’s location bar and by the padlock icon in the bottom status bar of your browser. FTPeS is basically the same thing. FTPeS uses the same type of technology to encrypt your login credentials as you connect to the FTP server. This prevents anything that might be listening on your connection from reading your username and password. Regular FTP will pass this information across your connection in plain text, so if someone was sniffing your connection, they could easily attain your username and password.