US > Canada: Withholding Tax

thanks for your input @ iniside

Although, now I’m completely confused on what the withholding tax is. Why would Epic write about :

By country-specific withholding tax don’t they mean from their payment from THEM to YOU? So wouldn’t that be Canadian(or whatever other country) withholding tax? So what does the US withholding tax have to do with ? and How would an ITIN even help since the content creator is not the one paying Epic rather the other way around? Am I even understanding correctly?