You should seek prior authorization from the Director-General before agreeing to give the lecture. Even if you receive authorization, you may not derive personal benefit from the activity because it is connected to your expertise at CERN. The Finance and Procurement Department should invoice the event organizer for the agreed remuneration plus any additional costs to CERN, such as travel or per diem expenses. Furthermore, you should inform your Departmental Planning Officer in order to make the relevant financial arrangements.