Subscription issue with BritBox

I have a BritBox subscription - I signed up through the Apple TV app (on Roku) and have been using it successfully for quite a while. Today when I tried to access I was prompted to subscribe. I checked my account and (1) I have a receipt that shows I have an active subscription and (2) in the account section of the app it does show an active BritBox subscription. What do I need to do to get the BritBox to actually let me watch the shows? I'm wondering if I need to cancel and restart my subscription.