If you can't make or receive FaceTime calls
If none of the above reasons apply to you, and you still can't make or receive FaceTime calls, follow these steps:
Make sure that your device has a Wi-Fi connection to the Internet or a cellular-data connection.
Learn more if you're using router, firewall, or security software that restricts Internet access.
If you're trying to use FaceTime over cellular, make sure that Use Cellular Data is on for FaceTime. Go to Settings > Cellular > Use Cellular Data For, and turn on FaceTime.
Go to Settings > FaceTime and make sure FaceTime is turned on.
If you see "Waiting for Activation," turn FaceTime off and then on again. Learn what to do if you can't activate FaceTime.
If you don't see the FaceTime setting, make sure that Camera and FaceTime aren't off in Settings > General > Restrictions.
Make sure that you have the correct phone number or email address listed.
Go to Settings > General > Date & Time and turn on Set Automatically.
Restart your device.
Update your device to the latest version of iOS.