General FTP instructions are here: https://galaxyproject.org/ftp-upload/
These should work for most Galaxy servers, but each can configure things a bit differently. You'll need to contact this servers administrators directly to find out if there is a server problem (known or new). I don't see contact information at the hosted website or in the server summary in the Galaxy Hub, so instead try the authors of the related publication.
- Galaxy Public Servers: https://galaxyproject.org/public-galaxy-servers/ >> https://galaxyproject.org/public-galaxy-servers/a-game/ >> Citation(s)
Thanks, Jen, Galaxy team