Connecting LTE Router to Orbi

First, the basics:

There may be more than one Mofi LTE modem/router.  I found the User Guide for the Mofi 4500.  Page 8 indicates that the WAN port is to connect a cable or DLS modem (i.e. not use the LTE capability.  Or, perhaps it is designed to use LTE as "failover" if the primary modem fails.)

So, the Orbi's WAN (yellow) port should be connected to one of the Mofi's LAN ports.

The Mofi is a combination modem/router/WiFi device.  What should happen when the Orbi is connected to the Mofi is the Orbi will connect and get an IP address from the Mofi.  Acting as a router, the Orbi will then assign IP addresses to any device which connects to the Orbi, either the LAN ports or the WiFi.

This can create quite a complicated situation.  The Mofi will be broadcasting one WiFi name and the Orbi will be broadcasting a different WiFi name.  Most people would turn off the Mofi WiFi capability, thus reducing the radio interference.  Most people would also want to have only a single router assigning IP addresses.  Either the Mofi needs to be put into "passthrough" mode or the Orbi should be put into Access Point (AP) mode.  Using the Orbi web interface, this is on the Advanced Tab->Advanced Settings->Router/AP Mode.

Diagnosing the problem:

When the Orbi is connected to a Mofi LAN port and powered on, the "Ring Light" at the top should go through a series of colors:

https://kb.netgear.com/31030/What-do-the-LEDs-on-my-Orbi-mean

When the Orbi ring light finally goes out, you should be able to do three things:  (1) on the management interface of the Mofi, the Orbi should appear as a device on the Mofi LAN port, (2) if a computer (PC, Mac, laptop) ethernet cord is connected to one of the Orbi LAN ports, it should reach the internet, and (2) the Orbi should be broadcasting the WiFi name that is printed on the label (on the bottom) and the WiFi password should match what is on the label.

Please let us know if any of this works out in your situation.