If you’ve set up a PPTP VPN server, iOS 10 and macOS Sierra users won’t be able to connect to it. iOS 10 and macOS Sierra will remove PPTP connections from any VPN profile when a user upgrades their device.
Even though PPTP protocol is still available on iOS 9 and earlier or OS X El Capitan and earlier, we don’t recommend that you use it for secure, private communication.