When you sign in with evoseedbox, you create an account and opt for a Seedbox. This seedbox is a remote server space with its own username and password.
Therefore the FTP credentials are not the same as your Evoseedbox credentials.
Your FTP credentials are available in the client area of your seedbox. Using these credentials, you can access all the applications, connect with your seedbox using FTP clients like Filezilla, and much more.