Wifi network extenders and ISP provided mesh-ready routers

I just fought getting a 3rd party range extender working and wanted to share what I learned.

Equipment:

Macard re1200 range extender and Gigaspire blast u4 GS2028E router

After setup of the Macard extender, all 3 lights were solid green meaning that it connected and authenticated to the router. However, devices connected (wirelessly) to the macard could not access the internet.

What I found that fixed it was I had to enable the "ARP spoofing" security flag in the Gigaspire's settings. The initial user ID and password are printed on the label on the back of the router so use that to log in.