AdvertisedId: The identifier of a beacon as advertised by it. This field must be populated when registering. It may be empty when updating a beacon record because it is ignored in updates. When registering a beacon that broadcasts Eddystone-EID, this field should contain a "stable" Eddystone-UID that identifies the beacon and links it to its attachments. The stable Eddystone-UID is only used for administering the beacon.