I signed up to HBOnow on Roku, but not able to access it on my cell either through the Roku app or directly on the HBOGO app. Any advice Please?
Welcome to the wonderful world of AT&T's HBO confusion.
HBO Go is for cable/satellite subscribers and is tied to that subscription.
HBO Now (I think) is being replaced by HBO Max.
HBO Max is the new one, but there is currently no agreement with Roku or Amazon yet.
To be honest, don't subscribe through Roku or other third parties if possible. Subscribe directly with the various services. They get 100% of the money, and you are free to use whatever device you want.