To watch BT Sport you need to use the TV Anywhere app and select a channel with the streaming symbol next to it e.g. 531 if you haven't used that device before to watch anything you'll be asked to register the device. You need to be connected to WiFi to watch
As clerom has stated, you need to be connected to WiFi to use our TV Anywhere App. Connect to WiFi and try playing the channel again. If you're still having trouble watching after that, give me a shout and I'll take a look for you.
All the best :d
Tech fan? Have you read our Digital life blog yet? Check it out