PPTP VPN for dedicated IP

[axiom]

I have subscribed to a dedicated IP provided by my VPN provider.
To use it, I need to connect to a host via PPTP over my regular internet connection.

Anybody could help provide some guidance how?
I have set up a Point-to-Point device in the Interfaces tab already with the provided credential. However, I don't know how to proceed further. When I try to assign the device such as pptp1 that was created in the Assignments tab, it says "The interface "pptp1" does not exist. Make sure to apply its configuration first." But maybe that's not the right thing to do. I just don't know.

For those who concern about the security of PPTP. The requirement here is to only use the dedicated IP.

Thanks