Hi Aram,
The Tobii.EyeX.Client.dll needs to go directly in the root of your Unity project folder, and the Tobii.EyeX.Client.Net20.dll should go in the root of the Assets/Plugin directory.
There was no link to which instruction you had followed that said to copy to the Plugins/x86 and Plugins/x86_64 folders. Was that documentation from Unity?
Additionally, if you build and deploy your Unity project, you need to copy the Tobii.EyeX.Client.dll to the same directory as the game’s executable (“.exe”). We are working on getting this into the build process, but for now this step has to be done manually.