Using Windows Connection Manager based VPN on macOS
It seems a similar question (connecting to SSTP VPN) is answered here:
How to connect OS X Yosemite to a Windows based SSTP VPN?
and here:
https://stackoverflow.com/questions/40590806/windows-sstp-vpn-connect-from-mac/40590807#40590807
Especially on the last one, ppl seem to have succeeded in connecting.