if you could please make sure the apple firmware has been updated on your devices, Apple have performed a release today, (11.3) which might be crashing the NOW TV app
As a work around please follow these steps:
Restart Apple TV 2. Launch NowTV app - it will crash once 3. Launch NowTV app again 4. DO NOT use the settings - Sign in to NowTV - it will crash the app 5. Select and play a piece of contnet 6. NowTV app will ask you to sign in to account 7. Accept T&Cs 8. Sign in as normal.