I'm running a raspberry pi server. With port forwarding I can reach it over port 22 and 80 from anywhere, over the internet. 

I'm trying to add SSL to the website I'm hosting on there. When trying to port forward port 443, it gives the following error: 

4937

The IP address is not in the same subnet with LAN IP address. Please input another one.

I do not know what this error means, or how to solve this.