Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
I subscribe to Cinemax via Prime Video. I can watch it on my laptop, but not on my Roku. On the Roku it wants me to sign up for the subscription. All other channels subscribed through Amazon work fine.
For more information about that channel's account authentication and functionality, you'll want to contact the channel provider support directly to inquire further. Many channels on Roku are developed and maintained by the channel provider themselves.