I am having trouble accessing my Windows 10 IIS-hosted website from the Internet, but I am able to access the website via the LAN at http://192.168.0.3:81

On the IIS server, IPConfig gives the IP 192.168.0.3

The IIS webpage is bound to port 81

The public IP 101.100.131.63

I have set my TP-Link AC1750 up with the following port forwarding rules (NAT is enabled, so is Hardware NAT), and have rebooted after setting these:

Accessing http://101.100.131.63:81 gives nothing but timeouts, but pinging 101.100.131.63 gets a reply.

My ISP is MyRepublic, UFB

I just can't get the website accessible over the Internet, and I could really do with suggestions on what to try next. I've tried setting remote access to my router's web interface to be accessible from any IP and connecting to that at the configured port, but get the same timeouts. I've tested with a few online port scanners, which say port 81 is closed.

I'm starting to think there may be some ISP-level filtering going on. Does anyone have any ideas on what to try next?