I just purchased and setup my first Roku TV and added Netflix and Prime Video channels to my account. I keep trying to launch both channels to enter my login credentials, and finish the setup. It looks like it is launching the channel for a few seconds, but then reverts back to the home screen.
I already had subscriptions through the services. Your suggestion worked. Initially, I added the channels through the Roku website. This time, I added the channels through the smart tv and it allowed me to enter my credentials. Not sure if that was what caused the original problem, but thank you for your help!