I have a HBOGo subscription through my cable provider. When trying to link the account with the Nvidia Shield TV the provider is not listed, just mostly colleges.
Anyway, when I went through the activation I just selected "Samsung Smart TV" and put in the code. HBOGo activated on the Shield without issue and now can access the app right through the Shield instead of having to use my phone to cast.
Probably something a lot of you know already, but figured I'd share.
Dear God...
Do you have Comcast?