If you buy a premium subscription through Roku, you generally have to watch it on a Roku device or through the official Roku Channel app. You might not be able to use those credentials to log into that network's native app on a computer, smartphone, or competing device like an Apple TV.
Open the newly installed app. You will see a prompt to start a free trial or purchase a subscription directly using your linked Roku account payment method. Through The Roku Channel App how to buy channels on roku
Click on the network banner you want to add and follow the on-screen prompts to confirm the recurring monthly purchase. If you buy a premium subscription through Roku,