Trying to set username variable in batch script

Hi,
So my server requires the username in the format: www.domain.com/email@address.com

This seems to cause problems when I attempt to put it all on the one line:
So I found another forum post where it is mentioned to use a variable for the username, by adding this line to the script:
and then using %USERNAME% for the open script:
When I try to run this it returns 'unknown command 'set'.'

My batch file is just simple:
and contents of script.txt:
Any help appreciated!

The set command should be in a wrapping batch file, not in WinSCP script.
But it won't help you anyway. It makes no difference if you specify the username directly or via environment variable.

Solution is to URL-encode the slash and at sign:
See https://winscp.net/eng/docs/session_url

Edit 2021: Now you can easily use -username switch that does not need any encoding:
https://winscp.net/eng/docs/scriptcommand_open#username

Thank you so much prikryl – URL-encoding the slash and @ symbol worked like a treat. Greatly appreciated! :D

Nick