I've recently upgraded my MacBook Pro to macOS High Sierra Version 10.13. So did my friend. We called each other on FaceTime. It took several attempts to establish a FaceTime connection. The first few times the call disconnected immediately when I hit the answer button. It didn't use to be this way before the upgrade. Is there anything I can do to fix this issue?
Here's a link that might shed some light on that issue. http://support.apple.com/kb/TS5419 D.
Turn Facetime off and then back on. Make sure it activates and then restart your device.
Also make sure that both of you check your Wi-Fi quality. If you are streaming video or playing video games in the background, your internet speeds will be going to that specific task.
If that doesnt work then sign out of iCloud and then sign back in.