Sbg3300 - how to setup a PPTP VPN server on this router?

I'm trying to setup a PPTP VPN server on this router but don't know how to grant a particular user right to connect via PPTP. My settings for PPTP server are here:

The users settings are here:

Windows PPTP VP client tries to connect to the VPN server, shows 'Verifying password...' and after 30secs of waiting breaks connection with error code 619. What should I do to enable working of this PPTP server?

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