@Anonymous User
Welcome to the forum. You are allowed to watch NOW TV on up to two devices at the same time, however sometimes the system doesn't detect when a device stops watching straight away, you may need to wait up to 10 minutes before the system realises this and let's you watch on another device.
You can minimise the chance of this happening by using the back button on the remote (or X close button on other apps depending on device) to return to the NOW TV app rather than directly quitting the app whilst it is still streaming.
If you still have problems try signing out of any apps you've recently used (or website if you watch in a browser) and then sign back in again (you should be able to do this by going to the My Account screen in the NOW TV app).
