Hi @ozopled, apologies for the confusion. Within China, there are greater restrictions on the licencing model. However, if you are content to develop for interaction purpose then you are free to use the C# SDK We provide either as the Stream Engine API or Interaction Library API, although the stream engine would seem to be the most appropriate for your needs. So long as you do not intend to store the gaze data or use it for analysis, then no additional licence needs to be purchased. The requirement was, however, necessary to use the Python API of the Pro SDK.