Hi @me-supachai thanks for the clarification. We now understand that the issue is in using the Nuget package manager which is not be used for setting up the Stream Engine with Unity.
Rather, download the relevant DLL directly from https://www.nuget.org/packages/Tobii.StreamEngine/ -> “Download package”
Theareafter, unzip and setup references within Unity according to specified documentation @ https://docs.unity3d.com/Manual/NativePlugins.html
Hopefully this should be enough for you to get started, please let us know how you get on.