Welcome to the Roku Community, @lilliekelley!
Thanks for letting us know about this. We'd be happy to help you access the Paramount Plus app on your Roku streaming device.
If I understand your concern correctly, your subscription is billed via Roku, right? If so, you can try accessing it inside The Roku Channel to see if you can access it successfully.
You may also try installing the standalone app by navigating to your Home screen. Scroll down to select Streaming Store and search for Paramount Plus. After successfully installing this, try accessing it and see if that works.
For reference, you may visit this support article related to this: How to add apps to your Roku streaming device.
Please keep us posted on how it goes, and we'll go from there.
Best regards,
Carly
Carly Y.
Roku Community Moderator