I transferred to a new unit and my Flex box won't work

Hi, I transferred service to a new apartment and went through the channels to do so over the phone. When I plugged my Flex box in, all I get is the "Welcome, loading your experience" screen for about 15 seconds before the whole screen goes black. I'm not a new customer, just transferred service, so I assume the box should work with the account. However, when I log into my account now I don't see it listed under devices.