Cool idea, can only use 2D at the moment. Looks like the 3D tile quota is exhausted:
"message": "Quota exceeded for quota metric '3D Tiles root requests' and limit '3D Tiles root requests per day' of service 'tile.googleapis.com' for consumer 'project_number:1016378558728'."
https://tile.googleapis.com/v1/3dtiles/root.json?key=AIzaSyB...