Roku currently has two separate ways for subscribers to sign up to view STARZ content; the Roku Channels add-on service and a subscription through the STARZ App on a Roku device.
Roku, not STARZ, offers Roku Channels. Therefore, Channel subscriptions do not have access to the STARZ app. Instead, access the channel through Roku devices, the Roku channel website, and the Roku apps on mobile devices. Reach out to Roku support for help with any technical or authentication issues with the Roku Channel, app, or website.
A STARZ direct subscriber cannot access STARZ on Roku Channels. However, anyone can check which subscription they have by heading to https://my.roku.com/account/subscriptions. STARZ subscriptions will show as STARZ, while STARZ, through the Roku Channel subscription, will show as a Roku Channel premium subscription to STARZ.