If you still have this problem, this is what fixed it for me. Check if your Apple TV has failed the activation: go to Settings, General, About. At the bottom you should see Activation Failed, this is a new known bug. If this is the case, then this is why AirPlay is not working for you and here's how to fix it with a Mac or a PC:
If you have a Mac:
- Download Apple Configurator 2 for free from the App Store (it's an official Apple app)
- Connect the Apple TV to power and wait for the led to stop blinking (full boot)
- Connect the Apple TV to the Mac with a standard Micro USB cable
- Open Apple Configurator 2 app and
- Wait for the Apple TV to show and double-click on it
- Choose Profile on the left
- Click on Activate and wait for the process to finish
- Unplug the Micro USB cable and plug the Apple TV to the TV with an HDMI cable
- Check again on Settings, General, About: the Activation row shouldn't be there anymore
- Try AirPlay again, it should work now
If you have a PC with Windows:
- Download and install the "3uTools" free software
- Connect the Apple TV to power and wait for the led to stop blinking (full boot)
- Connect the Apple TV to the Mac with a standard Micro USB cable
- Open 3uTools software
- Wait for the Apple TV to show
- Click More
- Click Batch activation
- Click All and Start and wait for the process to finish
- Unplug the Micro USB cable and plug the Apple TV to the TV with an HDMI cable
- Check again on Settings, General, About: the Activation row shouldn't be there anymore
- Try AirPlay again, it should work now
[Edited by Moderator]