How can I resolve 'Software Update Required' error for Apple TV app on Fire TV?

Error Using AppleTV App on Fire TV - Help???

I downloaded the AppleTV app on my Fire TV, but am receiving an error message "Software Update Required: To use AppleTV app, please install the latest Fire TV software version in Settings" There are no updates available in Settings - what next? I don't want to subscribe to Apple TV if I can't watch on my TV... all other apps (e.g. Netflix, Prime Video, Disney+) work...

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