Please add ftps to commands. There are ftpput, sftp`, rsync, but not ftps.
For example Synology backup server doesn't allow to log by ssh users which are not admin. This means there is no way to login without manually writing password with sftp or rsync etc. So there is no way to have automatic backups. This commands work well with ssh keys, but while for security reason ssh is turned of on backup server, then you can use only ftpput. But here is another problem, ftpput doesn't use SSL / TLS which is unsafe and turned off by default too. The only one reasonable choice which is secure is ftps which is not in VyOS commands available to use.