Unless you are using the 3 network for your internet.
I had endless problems last year trying to get GCN app to work properly via Chromecast with 3 as my ISP
It sort of worked, some of the time. Same issue with Eurosport Player too.
I also had some issues with BBC Iplayer on 3 so it was obviously a 3 problem.
They may have fixed it but given that 3 refused to recognise a problem, I doubt it.
I tried a Vodafone sim, and everything worked perfectly.
Then I move to Tesco Mobile, and everything works perfectly with them too.