OSX server 5.2 VPN type missing
OS X Server 5.2 only supports L2TP/IPSec VPN. 

Apple has dropped support for PPTP for security reasons. PPTP is known to have a number of significant security vulnerabilities.

Apple started to warn their users in OS X El Capitan and iOS 9 during VPN client setup not to use PPTP any more. With macOS Sierra and iOS 10, Apple has removed PPTP client support.

If, for some reason, despite of the security problems, you need to continue to use PPTP, you will probably need some third-party software. But you should not.