The main cause of the 530 error in the FTP client software is an error in the FTP connection information.
(Screenshot is from FFFTP)
In order to make an FTP connection, you will need your FTP username and password, not your cPanel login information.
Please refer to the "FTP connection information" in the "[mixhost] server account setup completion notification email" sent to the email address you registered when you registered the server account, and check if you can log in.
If you cannot find the email, please contact customer support.