@worldaccordingt-
I have no inside knowledge of how this is supposed to work, but ...
Assuming your purchased your subscription directly from Weather4Us, Weather4Us would be the ones tracking whether you have a subscription or not. You should be able to log into the Weather4Us app on Roku -- using the credentials you established with Weather4Us when you registered (normally email address and password).
I found this page on the Weather4Us site, which may be of some help: https://weather4us.com/plus/
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
If this post solves your problem please help others find this answer by clicking "Accept as Solution.".
Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X
