I hope you're doing well.
Channel logins or authentication are handled directly by the channel developer. We suggest reaching out to NBC support to report the issue and for further help. They can resolve the error you are having with channel authentication.
You can contact them here: https://help.nbc.com/hc/en-us/requests/new?brand=nbc
Thank you for your understanding.
All the best,
Roku Forum Moderator