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.
If I understand correctly this unnamed certain channel has some free content and other content that requires a paid subscription. You already are paying a specific subscription fee for this channel on your cable or some other account.
In many (most? all?) cases when you subscribe to a premium channel via one provider you can only view it on that provider.
If instead you subscribe directly with the channel on its website, you should be able to view the channel on any system that offers it (computer browser, phone, streaming system, etc.).
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T