FISH shell support in WinSCP

Could not scp a file because I am using a fish shell. Can you change this?

I know little about fish shell, but most likely it's incompatible with WinSCP requirements:
https://winscp.net/eng/docs/requirements#scp

Did you try to configure WinSCP to use bash explicitly?
https://winscp.net/eng/docs/ui_login_scp

Or why do you even use SCP? Did you try SFTP?