Hi @h-moon and thanks for your query. It looks like you are using the older Tobii Core SDK C# SDK for your project? This software has been deprecated quite some time and has now been replaced with the Tobii Interaction Library, which also supports the C# language.
We provide a very detailed tutorial and several samples of this new API available @ https://developer.tobii.com/consumer-eye-trackers-interaction-library-getting-started/
If you kindly go through the C# section on this page and get back to us if you still are experiencing issues. Best Wishes.