Port Forwarding a Port Forward?

I have a system setup with Comcast Business that includes an all-in-one into a fortigate. We handle all the portforwarding etc on the fortigate. I have one problem though, none of my port forwards actually work.

The way it works now is that behind the fortigate I have a server running nextcloud and I want my users to be able to access this. On the fortigate, i have a port forward setup to go from the fortigates wan port 445 to the 10.1.5.67 address port 443.

On the comcast all-in-one, i am then forwarding the real wan connection to the static IP of the fortigate on port 445.

This isn't working at all though.

Any and all help is appreciated!