Can logon via GUI but not cmd line due to "@" on username

Hi,
I am trying to create a batch file to transfer files between my company and an external host. This batch file will run as a scheduled task on a Windows 2008 server.

My external contact has provided me with the details, which is similar to below

Server: server.com.au
Username: server.com.au/sii@abc.com.au/dw
Password: abc123

Using the GUI, I can logon fine

However, If I try to logon from winscp.com using this command
open sftp://server.com.au/sii@abc.com.au/dw:abc123@server.com.au:22
I receive a prompt to add the username and password, which gives me an access denied message/

I am suspecting that this is because of the @ sign on the user name. If this is the case, could you please advise how I can push this through via a command line?

Thanks

It's actually the slash, not the at sign. But it's better to URL-encode both.
See https://winscp.net/eng/docs/session_url

Thank you Martin, I replaced the special characters as advised and it worked.