Hi @owenatkinson and thanks for your query. We are working on porting the latest stream engine v3 onto Nuget and hope to have this available soon.
In the meantime, you can download the latest stream engine directly @ https://developer.tobii.com/consumer-eye-trackers/stream-engine/getting-started/
In addition, we have created a migration guide for users of the 2.x Stream Engine which discusses the various changes you need to take into account for proper operation including avoiding the callback errors.
Kindly view this @ https://tobii.github.io/stream_engine/migration_guide_2.x_to_3.x
Do let us know if we can provide any further information. Best Wishes.