I had already given up using Opnsense in favor of Pfsense for a Windows PPTP server a few months ago.
Now I try again with Opnsense, and, like on previous version, the connection is established but gets dropped after 10-15 seconds or so, when traffic starts flowing.
I have 2 incoming rules enabled, one for GRE, one for tcp port 1723.
By design?
I think I know now...is because Opnsense is connected to a router who ports forward...but this device has no way of treating GRE, required for pptp.
Opnsense is great anyway...