It’s because the tool is using a WQL query in the backend to find the user and ‘’ is a special character. You can use domain_username, domain\\username or %username to find the user as a workaround. We’ll try to make the user experience better in a future version.
Look forward to improvements there - but even stating on the powershell window the format would be a massive improvement - It is impossible to use without this knowledge, so just state it in the window surely?