>MX 68 Public ip is different and MX ip is private IP 192.168.1.0/24
For that case, you'll need to configure the device that has the public IP to forward UDP/500 and UDP/4500 to the MX WAN interface.
Also note that if the user is on 192.168.1.0/24 at home that it may not work (seems to work sometimes and not others).