Port Forwarding

I am setting up port forwarding on a R7000 router.  

I have successfully opened the 3389 port for RDP access.

I now need to open Port 80 for access to a "web site".  It's really just a CRM ported to html for remote access.

From the desktop where it's installed, I can open the web site (localhost/apfw).  From other computers inside the network, I can acess the web site. (computername/apfw).

From outside the network though I get no joy. 

Canyouseeme.org reports "I could not see your service on xxx.xxx.xxx.xxx on port (80)
Reason: Connection timed out"

If I check with port 3389, it is successful.

Yes, I have opened the port in Advanced Setup.  This router is running behind a Comast/Xfinity Gateway.

Any ideas on why I an not getting the request to the server (Windows 10)???  Comcast was no help.  Sofware vendor was also no help.  Why would Port 3389 work fine, but not Port 80???

Thanks!

Chris