Unable to connect NETGEAR Extender EAX15v2 to home wifi

When attempting to connect new extender to our WiFi modem (ZTE - model H268A) via Nighthawk app, it gets all the way to the point of entering password of our WiFi, then says the password is incorrect. The password being entered is 100% correct. Are the 2 devices just not compatible? Our internet provider has suggested maybe the modem and extender are not compatible?