Use the Pwd action from the SFTP module and use the string it returns as prefix, or use './', that is a dot and a slash. You're prefixing the destination with '/', a slash, which points to the root of the destination server file system, to which you don't have access. So you enter e.g.:
$Pwd + '/' + $CSVFile/Name
Normally when you connect to an external SFTP server you already end up automaticly in your home directory. So you can leave it empty. But when you want to have subdirectories in that home directory you can specify the subdir where you want to put the file.
Regards,
Ronald