Diagnosis
A red Internet LED means the router cannot establish a connection to your modem or to your Internet Service Provider (ISP). The physical link is likely down.
How to Fix It
1) Power cycle both devices. Unplug your modem and your BE800. Wait 30 seconds. Plug the modem back in and wait for all its lights to settle. Then plug the router back in. 2) Check the cable. Ensure the Ethernet cable is firmly plugged from your modem's output port into the blue WAN port on the back of the BE800. Try a different cable if you have one.
If That Didn't Work
Your ISP might require specific settings like PPPoE or VLAN tagging. You'll need to log into the router's web interface (tplinkwifi.net) and go to Advanced > Network > Internet. You may have to clone your MAC address or enter PPPoE credentials from your ISP.
Heads Up
If you previously had another router connected, your ISP might be locking onto that old router's MAC address. The 'Clone MAC Address' button in the internet settings often solves this instantly.