Searching BritBox

How can I search BritBox when watching through Apple TV on a Roku stick?

I subscribed through Apple TV. There is a search feature in Apple TV which allows me to search for shows that I know are on BritBox. However when I click on my search results it wants me to log into BritBox with a separate ID.

However when I open the BritBox app through Apple TV, there is no search option allowing me to go directly to the show. Instead I have to scroll through shows to find the one I want to watch.

I am starting to think the only solution is to cancel the subscription through Apple TV and subscribe to BritBox directly but surely this cannot be right.

Any suggestions?

Thanks.