Hi @ipsych and thanks for getting in touch. Indeed, if you intend to use the Tobii Pro SDK in conjunction with the Tobii 4C Eye Tracker, then this requires the purchase of a special analytical licence to do so (which comes with a special unlock file to grant access to gaze data)
To read more about this and receive a quote please follow the link @ https://analyticaluse.tobii.com/
Do let us know if we can provide any further information.