You do not have to show your face. However, this is "video", it is a visual media, and students want to have a relationship with their teacher. They want to know and trust their teacher. If you look at the best selling courses and how the instructor communicates, particularly in the promo video, you will see that speaking directly to your audience is definitely an advantage.
No one can say definitely that your course won't sell without showing your face. But, as a new instructor, with lots of established competition, you need to take every advantage you can.
Lawrence M. Miller