how do i fix error code n8109 on netflix?

Netflix uses Silverlight for content protection, so I would start by uninstalling that, then reinstalling it.

Uninstall Silverlight: https://www.microsoft.com/getsilverlight/get-started/install/removing-silverligh t-mac.aspx

Reinstall Silverlight: https://www.microsoft.com/getsilverlight/Get-Started/Install/Default.aspx

Also I would run through these Steps to tune up your machine.

..Step by Step to fix your Mac