Nighthawk app won't recognize extender

My extender is plugged in with green light showing that my phone is set to the wifi connection of NETGEAR_EXT, but when I try to have the nighthawk app find the extender, I get the message that the extender can't be found. It says I am connected to NETGEAR_EXT. Go to WiFi and connect to NETGEAR_EXT. I 've tried factory reset, uninstalling the app, two different routers. This should have been an easy fix, but nothing is working. Can someone help me, please?