Diagnosis
The red internet LED means the router can't establish a WAN (wide area network) connection to your modem. It's a handshake issue between the two devices.
How to Fix It
Power everything down. Unplug the modem, router, and any other network gear. Wait 60 seconds. Plug in and turn on just the modem first. Wait until all its normal lights are solid. Then, connect the modem to the router's WAN port (the blue port) with an Ethernet cable and plug in/turn on the router. This sequence forces a fresh IP address pull from your ISP.
If That Didn't Work
Log into the router's web interface (192.168.50.1). Go to WAN > Internet Connection. If your ISP requires specific settings (like PPPoE credentials, VLAN ID, or DHCP query frequency), you need to enter them here. A call to your ISP's support can confirm if special settings are needed.
Heads Up
Some modems (especially combo modem/routers) need to be put into "bridge mode" to work correctly with a third-party router like the AX86U, otherwise you get a double NAT conflict.