Your Arlo SmartHub or base station serial number might not auto-populate during a new system setup because of the following:
The mobile device or computer that you're using to register your base station isn't connected to the same network as your base station. When you connect your base station to your router using the provided Ethernet cable, it automatically connects to the local network in your home or business. The mobile device or computer that you're using to register your base station must be connected to the same network.
Your base station is already registered with another email address. You must use the email address that you initially registered your base station with. If you want to use a different email address, you must reset the base station.
Your base station is registered to someone else or an account that you don't have access to. If you bought your Arlo system from another user who didn't remove it from their account, reset the base station.