PPTP connects from LAN but not from WAN

Question

I want to set up a PPTP connection for client remote access in a Sophos XGS138 (SFOS 21.0.0 GA-Build169) 
 When trying from LAN, the connection is established properly. Incoming address is the ISP Router internal address (192.168.10.1) performing a Loopback operation. 
 When trying from WAN, I get the following messages: 
 LCP: Negotiation Opening for x.x.x.x 
 FSM: Disconnect due to LCP timeout 
 LCP: Negotiation Closed for x.x.x.x 
 Port forwarding and NAT to the XGS is set. 
 What is missing?

PhilippRusch · Answer

Hello Rolf, 
 the most simple and quick solution when it comes to VPN with a Sophos firewall for us is to use SSL-VPN with a local user account at the firewall.

LuCar Toni · Answer

You are in the wrong field: You are looking in SSLVPN Site to Site, you need to look for Remote Access. Remote Access SSLVPN will generate OVPN. You need to download the SSLVPN config from the VPN Portal (as it is remote access). There you will get the SSLVPN OVPN File. 
 The APC is for site to site and not usable (applicable) for your scenario.