Hello tomdotw,
Thank you for reaching out. Let's sort this out. However, to be able to understand the issue better, can you give us more details by answering these following questions:
• Were there any error messages when you attempt to register your Surface Book 2?
• Since you mentioned that the device is a prototype, can you send us an image of it so we can have it checked on our end?
Also, to know the serial number of the Surface, you can check this link for more information.
Keep us posted at your most convenient time.