Hi Raerae, welcome to the forum and thanks for posting. Sorry you are getting an error when trying to watch BT TV.
Are you getting this error on the BT TV box or when trying to watch via the app?
When was your BT TV service activated?
Are you connected via Ethernet from the hub to the BT TV box or are you using adapters?
Is the error code BTP-15000?
If so the advice for this error on BT TV Error Codes is to reboot your TV box by flicking the switch at the back and retry the service.