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  steps :

Login to   WHM

Go To : Service Configuration

Then click  on : FTP Server Configuration

and  then check that  :

TLS Encryption Support :  is set to  “Optional”

if  not then set it to  “Optional”

That’s  all this will do it.