As mentioned out in the comments, hairpinning (NAT Loopback) support on your router(s) could be an issue:
Hairpinning is where a machine on the LAN is able to access another machine on the LAN via the external IP address of the LAN/router (with port forwarding set up on the router to direct requests to the appropriate machine on the LAN).
The quickest way to test for this issue is to use a network that isn't local to access your domain. For instance, connect your smartphone to your carrier network (not WiFi) and see if you can use the mobile browser to successfully access your the web server via your domain. If you can, then the problem you are encountering locally is likely a hairpinning issue.
If hairpinning is the issue, then you could (potentially) run a local DNS server (such as e.g. BIND) on your network to solve this, or even possibly buy a new router.
I tried port forwarding from the ISP Router to my third-party router (TPR) but I still get sent to my ISP router setup.
To confirm, the setup should likely be:
Also, assuming your diagram is accurate, it might be worth considering ensuring your devices are all on the same network (
192.168.0.x are different networks with a default subnet mask of
In case I change the web server port to something different, would I have to do something else?
You probably won't know until you give it a try. But I would say that changing the port is would be another thing to test. Of course, if you do this, make certain the web server, any port forwarding and any firewall rules are set correctly to allow the connection.