@Hannahcat
First, some information that might be applicable.
With a Roku device (this is true for Amazon as well, but we're talking Roku for now) you can log in to an app one of two ways. You can subscribe through Roku, paying Roku for the subscription, and watch on any Roku device that is tied to your Roku account. The downside is the subscription is only valid on Roku. You can't use it on another streaming device, on a phone, or on a tablet. Roku is the only place the subscriptions is valid.
The other way is the traditional way. You go to the service Website -- in this case https://www.paramountplus.com/ -- and subscribe there. You would then use those credentials to log on on the Roku device.
Note you can do both, but that's really a waste of money. Don't do both.
If you have a subscription, you likely have it one of those two ways. Either of those ways will work on your Roku device. Which way did you subscribe, and what's happening on the screen -- exact working; pictures help -- when you try to watch the service.
DBDukes
Roku Community Streaming Expert
Note: I am not a Roku employee.
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