Offering in-channel accounts and purchasing products off-platform.
Developing SVOD channel on Roku using OTT platform.
Any payments for in-channel products must be completed on-device.
The Application Distribution Agreement states "Public Applications that are Pay-To-Install Applications, Subscription Applications or Transactional Applications must use Roku Billing Services" (section 3.1 of Commercial Terms Exhibit).
You may not redirect users to sign up off-device for a subscription or any other paid content service that is available in your Roku channel.