Netgear EX6120 wi fi extender won't accept password to connect iPhone 10 keeps saying invalid passwo

Did you just set it up? 

Any special characters in the ssid/password?

Have you tried logging into the extender to see if maybe the password is wrong?

Also, try forgetting the ssid/password on your iphone and re-entering the info. autofills have been known to overwrite what's been typed in.