In the Windows computer you want to access, when prompted, you must insert the username and password that you usually use to log in to that computer, the same account you would use if sitting in front of it. It can be any of the formats here:
Pin numbers are not accepted.
Quoting from the article: Because of Windows policies, the password cannot be empty when connecting by remote. The PIN cannot be used as well. It’s necessary to set a password for entering by remote.
To do that (on Windows 10):
– Click the Start button -> Settings
– Click Settings
– Select Accounts -> Sign-in and create a Password for your account.