Apple has removed support for PPTP VPNs in macOS Sierra. Thus, you will no longer be able to connect your PPTP VPN via Apple’s built-in VPN client on macOS Sierra.
In this regard, we’d like to remind you that our VPN client Shimo supports PPTP VPN and many other VPN protocols on macOS Sierra. Please make sure that you are using the latest Shimo version. You can download it here: Download Shimo