Can I use SHOWTIME streaming service on my Apple TV even though I subscribed elsewhere?

Yes, if you've previously subscribed on an Apple mobile device:
1. Go to the Apple TV main menu and launch SHOWTIME.
2. Select 'Restore Now' and sign in with your iTunes credentials.

If you've previously subscribed on a Roku device:
1. Go to the Apple TV main menu and launch SHOWTIME.
2. Select 'Sign In' and enter your SHOWTIME credentials.